US20120091652A1 - Sheet conveying apparatus and image forming apparatus - Google Patents
Sheet conveying apparatus and image forming apparatus Download PDFInfo
- Publication number
- US20120091652A1 US20120091652A1 US13/249,399 US201113249399A US2012091652A1 US 20120091652 A1 US20120091652 A1 US 20120091652A1 US 201113249399 A US201113249399 A US 201113249399A US 2012091652 A1 US2012091652 A1 US 2012091652A1
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- United States
- Prior art keywords
- sheet
- rotation
- rotation detection
- flag
- detection portion
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65H—HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
- B65H7/00—Controlling article feeding, separating, pile-advancing, or associated apparatus, to take account of incorrect feeding, absence of articles, or presence of faulty articles
- B65H7/02—Controlling article feeding, separating, pile-advancing, or associated apparatus, to take account of incorrect feeding, absence of articles, or presence of faulty articles by feelers or detectors
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65H—HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
- B65H2404/00—Parts for transporting or guiding the handled material
- B65H2404/10—Rollers
- B65H2404/14—Roller pairs
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65H—HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
- B65H2553/00—Sensing or detecting means
- B65H2553/40—Sensing or detecting means using optical, e.g. photographic, elements
- B65H2553/41—Photoelectric detectors
- B65H2553/412—Photoelectric detectors in barrier arrangements, i.e. emitter facing a receptor element
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65H—HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
- B65H2553/00—Sensing or detecting means
- B65H2553/60—Details of intermediate means between the sensing means and the element to be sensed
- B65H2553/61—Mechanical means, e.g. contact arms
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65H—HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
- B65H2701/00—Handled material; Storage means
- B65H2701/10—Handled articles or webs
- B65H2701/13—Parts concerned of the handled material
- B65H2701/131—Edges
- B65H2701/1311—Edges leading edge
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65H—HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
- B65H2801/00—Application field
- B65H2801/03—Image reproduction devices
- B65H2801/06—Office-type machines, e.g. photocopiers
Definitions
- the present invention relates to a sheet conveying apparatus and an image forming apparatus having the same, and more particularly to an image forming apparatus having a sheet conveying apparatus which can detect a leading end position of a sheet to be conveyed.
- the image forming apparatus provides a sheet conveying portion with a sheet detection portion detecting a leading end position of a sheet in order to match the time to send the sheet to an image transfer position with the time to send an image (toner image) to the image transfer position.
- the image forming apparatus provides the sheet conveying portion with a plurality of sheet detection portions to detect a sheet conveying state along a sheet conveying path such as a sheet conveyance delay and a jam (see Japanese Patent Application Laid-Open No. H09-183539).
- FIGS. 30 to 31B illustrate a conventionally general sheet detection portion.
- a conventional sheet detection portion includes a sensor flag 523 and an optical sensor 524 .
- the sheet detection portion is arranged on a downstream side in a sheet conveying direction of a sheet conveying roller pairs 518 , 519 closest to an image transfer position.
- the sensor flag 523 includes a rotating shaft 527 rotating the sensor flag 523 ; a light shielding portion 525 shielding an optical path L from a light emitting portion to a light receiving portion of the optical sensor 524 ; a stopper portion 526 positioning the sensor flag 523 to a home position; and a return spring 528 . Even if the sensor flag 523 rotates, the sensor flag 523 returns to the home position by its own weight or a pressing force of the return spring 528 .
- FIG. 31A illustrates a state in which the sheet is passing through and in contact with the sensor flag 523 .
- the sensor flag 523 returns to the home position illustrated in FIG. 31A .
- the light shielding portion 525 retracts from the optical path L, allowing the light receiving portion of the optical sensor 524 to receive light emitted from the light emitting portion again. Then, the sheet detection device recognizes that the trailing end of the sheet S has passed through the sensor flag 523 .
- the image forming apparatus has been required to meet user demand to further improve throughput. In order to improve throughput of the image forming apparatus, it is needed to increase a sheet conveying speed or shorten an interval from the trailing end of a preceding sheet to the leading end of a subsequent sheet (hereinafter referred to as a sheet gap). Consequently, the sheet detection device needs to return the sensor flag to the home position in a short sheet gap after the preceding sheet has passed
- the conventional sensor flag 523 operates such that when the leading end of the sheet S passed through the conveying roller pair abuts against an abutting portion, the sensor flag is pushed by the sheet S to rotate, and when the trailing end of the sheet moves away from the abutting portion, the sensor flag reversely rotates to return to a home position P. Consequently, the distance required for the sheet gap is a distance D 3 obtained by adding a distance D 1 from a position in which the trailing end of the preceding sheet passes through the abutting portion of the sensor flag to the home position P in which the leading end of the subsequent sheet abuts against the abutting portion to a distance D 2 between which the subsequent sheet is conveyed (see FIG. 31B ).
- the distance D 2 is a distance obtained by multiplying a time ⁇ t during which the sensor flag 523 moves across the distance D 1 by a sheet conveying speed V ( ⁇ t ⁇ V).
- V sheet conveying speed
- the present invention provides a sheet conveying apparatus inhibiting an increase in sheet gap distance while increasing a sheet conveying speed to improve throughput, and an image forming apparatus having the same.
- the present invention provides a sheet conveying apparatus including: a conveying portion configured to convey a sheet; a rotation detection portion rotatably provided and having an abutting portion which abuts against a leading end of the sheet conveyed by the conveying portion at a waiting position, wherein the rotation detection portion is rotated in a predetermined rotational direction by being pushed by the leading end of the conveyed sheet; a sensor portion detecting the conveyed sheet based on a rotational position of the rotation detection portion; a rotation transmission portion configured to transmit a rotational driving force to the rotation detection portion to rotate the rotation detection portion in the predetermined rotational direction after the rotation detection portion is rotated by being pushed by the leading end of the conveyed sheet; and an urging unit configured to apply an urging force to the rotation detection portion, wherein after the rotation detection portion is rotated by the rotational driving force of the rotation transmission portion, the urging unit applies the urging force to the rotation detection portion so that the rotation detection portion comes into contact with a surface of the sheet, thereafter the
- the present invention can shorten the time needed from when the sheet passes to when the rotation detection portion is positioned in the standby position, thereby reducing the need to secure a long distance required for a sheet gap distance and thus improving throughput.
- FIG. 1 is a sectional view schematically illustrating an entire structure of an image forming apparatus according to a first embodiment of the present invention.
- FIG. 2A is a perspective view illustrating a sheet detection portion supported by a paper feed frame according to the first embodiment.
- FIG. 2B is a perspective view illustrating the sheet detection portion viewed from an opposite side thereof illustrated in FIG. 2A .
- FIG. 3 is a perspective view illustrating a sensor flag of the sheet detection portion according to the first embodiment.
- FIG. 4A illustrates the sheet detection portion according to the first embodiment.
- FIG. 4B illustrates an assist cam and a rotation assist roller in a state illustrated in FIG. 4A .
- FIG. 4C illustrates an abutting portion of a shutter flag in a state illustrated in FIG. 4A .
- FIG. 4D illustrates a light shielding portion in a state illustrated in FIG. 4A .
- FIG. 5A illustrates a state in which a sheet abuts against the sensor flag.
- FIG. 5B illustrates an assist cam and a rotation assist roller in a state illustrated in FIG. 5A .
- FIG. 5C illustrates the abutting portion of the shutter flag in a state illustrated in FIG. 5A .
- FIG. 5D illustrates the light shielding portion in a state illustrated in FIG. 5A .
- FIG. 6A illustrates a state in which the sensor flag rotates to shield an optical path of the optical sensor.
- FIG. 6B illustrates the assist cam and the rotation assist roller in a state illustrated in FIG. 6A .
- FIG. 6C illustrates the shutter flag in a state illustrated in FIG. 6A .
- FIG. 6D illustrates the light shielding portion in a state illustrated in FIG. 6A .
- FIG. 7A illustrates a state in which the assist cam engages with the rotation assist roller.
- FIG. 7B illustrates the assist cam and the rotation assist roller in a state illustrated in FIG. 7A .
- FIG. 7C illustrates the shutter flag in a state illustrated in FIG. 7A .
- FIG. 7D illustrates the light shielding portion in a state illustrated in FIG. 7A .
- FIG. 8A illustrates a state in which the assist cam disengages from the rotation assist roller.
- FIG. 8B illustrates the assist cam and the rotation assist roller in a state illustrated in FIG. 8A .
- FIG. 8C illustrates the shutter flag in a state illustrated in FIG. 8A .
- FIG. 8D illustrates the light shielding portion in a state illustrated in FIG. 8A .
- FIG. 9A illustrates a state in which the abutting portion of the shutter flag abuts against the sheet and enters a wait state.
- FIG. 9B illustrates the assist cam and the rotation assist roller in a state illustrated in FIG. 9A .
- FIG. 9C illustrates the shutter flag in a state illustrated in FIG. 9A .
- FIG. 9D illustrates the light shielding portion in a state illustrated in FIG. 9A .
- FIG. 10A illustrates a state in which the trailing end of the sheet passes through the shutter flag.
- FIG. 10B illustrates the assist cam and the rotation assist roller in a state illustrated in FIG. 10A .
- FIG. 10C illustrates the shutter flag in a state illustrated in FIG. 10A .
- FIG. 10D illustrates the light shielding portion in a state illustrated in FIG. 10A .
- FIG. 11 is a perspective view illustrating a sheet detection portion supported by a paper feed frame according to a second embodiment.
- FIG. 12 is a perspective view illustrating a sensor flag of the sheet detection portion according to the second embodiment.
- FIG. 13A illustrates the sheet detection portion according to the second embodiment.
- FIG. 13B illustrates an assist cam and a rotation assist roller in a state illustrated in FIG. 13A .
- FIG. 13C illustrates an abutting portion of a shutter flag in a state illustrated in FIG. 13A .
- FIG. 13D illustrates a light shielding portion in a state illustrated in FIG. 13A .
- FIG. 14A illustrates a state in which the abutting portion of the shutter flag abuts against a sheet and enters a wait state.
- FIG. 14B illustrates the assist cam and the rotation assist roller in a state illustrated in FIG. 14A .
- FIG. 14C illustrates the shutter flag in a state illustrated in FIG. 14A .
- FIG. 14D illustrates the light shielding portion in a state illustrated in FIG. 14A .
- FIG. 15 is a perspective view illustrating a sheet detection portion supported by a paper feed frame according to a third embodiment.
- FIG. 16 is a perspective view illustrating a sensor flag of the sheet detection portion according to the third embodiment.
- FIG. 17A illustrates the sheet detection portion according to the third embodiment.
- FIG. 17B illustrates a sensor cam, a shutter spring, a cam follower, and a pressing member in a state illustrated in FIG. 17A .
- FIG. 17C illustrates an abutting portion and a light shielding portion of a shutter flag in a state illustrated in FIG. 17A .
- FIG. 18A illustrates a state in which the sensor flag rotates to shield an optical path of an optical sensor.
- FIG. 18B illustrates the sensor cam, the shutter spring, the cam follower, and the pressing member in a state illustrated in FIG. 18A .
- FIG. 18C illustrates the abutting portion and the light shielding portion of the shutter flag in a state illustrated in FIG. 18A .
- FIG. 19A illustrates a state in which the sensor cam engages with a rotation assist roller.
- FIG. 19B illustrates the sensor cam, the shutter spring, the cam follower, and the pressing member in a state illustrated in FIG. 19A .
- FIG. 19C illustrates the abutting portion and the light shielding portion of the shutter flag in a state illustrated in FIG. 19A .
- FIG. 20A illustrates a state in which the sensor cam disengages from the rotation assist roller.
- FIG. 20B illustrates the sensor cam, the shutter spring, the cam follower, and the pressing member in a state illustrated in FIG. 20A .
- FIG. 20C illustrates the abutting portion and the light shielding portion of the shutter flag in a state illustrated in FIG. 20A .
- FIG. 21A illustrates a state in which the abutting portion of the shutter flag abuts against a sheet and enters a wait state.
- FIG. 21B illustrates the sensor cam, the shutter spring, the cam follower, and the pressing member in a state illustrated in FIG. 21A .
- FIG. 21C illustrates the abutting portion and the light shielding portion of the shutter flag in a state illustrated in FIG. 21A .
- FIG. 22A illustrates a state in which the trailing end of the sheet passes through the shutter flag.
- FIG. 22B illustrates the sensor cam, the shutter spring, the cam follower, and the pressing member in a state illustrated in FIG. 22A .
- FIG. 22C illustrates the abutting portion and the light shielding portion of the shutter flag in a state illustrated in FIG. 22A .
- FIG. 23A is a perspective view illustrating a sheet detection portion supported by a paper feed frame according to a fourth embodiment.
- FIG. 23B is a perspective view illustrating the sheet detection portion viewed from an opposite side thereof illustrated in FIG. 23A .
- FIG. 24A illustrates the sheet detection portion according to the fourth embodiment.
- FIG. 24B illustrates an assist gear and a rotation assist gear in a state illustrated in FIG. 24A .
- FIG. 24C illustrates an abutting portion of a shutter flag in a state illustrated in FIG. 24A .
- FIG. 24D illustrates a light shielding portion in a state illustrated in FIG. 24A .
- FIG. 25A illustrates a state in which the assist gear engages with the rotation assist gear.
- FIG. 25B illustrates the assist gear and the rotation assist gear in a state illustrated in FIG. 25A .
- FIG. 25C illustrates the shutter flag in a state illustrated in FIG. 25A .
- FIG. 25D illustrates the light shielding portion in a state illustrated in FIG. 25A .
- FIG. 26A illustrates a state in which the abutting portion of the shutter flag abuts against a sheet and enters a wait state.
- FIG. 26B illustrates the assist gear and the rotation assist gear in a state illustrated in FIG. 26A .
- FIG. 26C illustrates the shutter flag in a state illustrated in FIG. 26A .
- FIG. 26D illustrates the light shielding portion in a state illustrated in FIG. 26A .
- FIG. 27 is a perspective view illustrating a sheet detection portion supported by a paper feed frame according to a fifth embodiment.
- FIG. 28 is a perspective view illustrating a sensor flag of the sheet detection portion according to the fifth embodiment.
- FIG. 29 illustrates the sheet detection portion according to the fifth embodiment.
- FIG. 30 is a perspective view illustrating a sheet detection portion according to a conventional image forming apparatus.
- FIG. 31A illustrates an operation of a shutter flag according to the conventional sheet detection portion illustrated in FIG. 30 .
- FIG. 31B illustrates an operation of the shutter flag according to the conventional sheet detection portion illustrated in FIG. 30 .
- the image forming apparatus is an image forming apparatus, such as a copier, a printer, a fax machine and a combined machine thereof, which has a sheet detection function of detecting a leading end of a sheet to be conveyed.
- the following embodiments will be described using an electrophotographic image forming apparatus 100 forming a four-color toner image.
- FIG. 1 is a sectional view schematically illustrating the entire structure of the image forming apparatus 100 according to the first embodiment of the present invention.
- the image forming apparatus 100 includes: a sheet feeding portion 8 feeding a sheet S; an image forming portion 14 forming a toner image; a fixing portion 10 fixing a transferred unfixed toner image; and a sheet conveying portion 9 as a sheet conveying apparatus. Further, the image forming apparatus 100 includes a sheet discharging portion 13 discharging the sheet S with the toner image fixed thereon.
- the sheet feeding portion 8 includes: a paper feed cassette 80 storing sheets S; a feed roller 81 feeding the sheets S stored in the paper feed cassette 80 to the sheet conveying portion 9 ; and a separation portion (not illustrated) separating the sheets S one by one.
- the sheet feeding portion 8 uses the separation portion to separate the sheets S stored in the paper feed cassette 80 one by one which is fed to the sheet conveying portion 9 by the feed roller 81 .
- the image forming portion 14 forms a toner image based on predetermined image information and transfers the toner image to the sheet S to be conveyed on the sheet conveying portion 9 .
- the image forming portion 14 includes: photosensitive drums 1 a , 1 b , 1 c and 1 d ; charging portions 2 a , 2 b , 2 c and 2 d ; exposure portions 3 a , 3 b , 3 c and 3 d ; developing portions 4 a , 4 b , 4 c and 4 d ; transfer rollers 5 a , 5 b , 5 c and 5 d ; and cleaning portions 6 a , 6 b , 6 c and 6 d .
- the image forming portion 14 includes a transfer belt 9 a.
- Each of the photosensitive drums 1 a , 1 b , 1 c and 1 d as an image bearing member is made by applying an organic photoconductive layer (OPC) to an outer peripheral surface of an aluminum cylinder.
- OPC organic photoconductive layer
- Each end portion of the photosensitive drums 1 a , 1 b , 1 c and 1 d is rotatably supported by a flange.
- a driving force is transmitted from a drive motor (not illustrated) to one end portion, the respective photosensitive drums are rotatably driven counterclockwise in FIG. 1 .
- the charging portions 2 a , 2 b , 2 c and 2 d uniformly charge respective surfaces of the photosensitive drums 1 a , 1 b , 1 c and 1 d by abutting respective roller-shaped conductive rollers against the respective surfaces of the photosensitive drums 1 a , 1 b , 1 c and 1 d and causing a power supply (not illustrated) to apply a charge bias voltage thereto.
- the exposure portions 3 a , 3 b , 3 c and 3 d irradiate laser beams based on the image information to form respective electrostatic latent images on the photosensitive drums 1 a , 1 b , 1 c and 1 d.
- the developing portions 4 a , 4 b , 4 c and 4 d include toner containing portions 4 a 1 , 4 b 1 , 4 c 1 and 4 d 1 ; and development roller portions 4 a 2 , 4 b 2 , 4 c 2 and 4 d 2 respectively.
- the toner containing portions 4 a 1 , 4 b 1 , 4 c 1 and 4 d 1 respectively contain black toner, cyan toner, magenta toner and yellow toner.
- the development roller portions 4 a 2 , 4 b 2 , 4 c 2 and 4 d 2 are adjacently arranged on the respective surfaces of the photosensitive members. Each development roller portion applies a development bias voltage to cause a color toner to adhere to respective electrostatic latent images on the photosensitive drums 1 a , 1 b , 1 c and 1 d to visualize the respective toner images.
- the transfer rollers 5 a , 5 b , 5 c and 5 d are arranged inside the transfer belt 9 a so as to abut against the transfer belt 9 a facing the photosensitive drums 1 a , 1 b , 1 c and 1 d respectively.
- the transfer rollers 5 a , 5 b , 5 c and 5 d are connected to a transfer bias power supply (not illustrated). A positive charge is applied from the transfer rollers 5 a , 5 b , 5 c and 5 d to the sheet S through the transfer belt 9 a .
- This electric field causes the respective negative color toner images on the photosensitive drums 1 a , 1 b , 1 c and 1 d to be sequentially transferred to the sheet S being in contact with the photosensitive drums 1 a , 1 b , 1 c and 1 d , thus forming a color image.
- the cleaning portions 6 a , 6 b , 6 c and 6 d remove a toner remaining on the respective surfaces of the photosensitive drums 1 a , 1 b , 1 c and 1 d after transfer.
- the photosensitive drums 1 a , 1 b , 1 c and 1 d , the charging portions 2 a , 2 b , 2 c and 2 d , the developing portions 4 a , 4 b , 4 c and 4 d , and the cleaning portions 6 a , 6 b , 6 c and 6 d integrally form process cartridge portions 7 a , 7 b , 7 c and 7 d respectively.
- the fixing portion 10 heats the sheet S with an unfixed toner image transferred thereto to fix the unfixed toner image.
- the sheet discharging portion 13 includes a discharging roller pair 11 , 12 conveying the sheet S with the image formed thereon by normal rotation or inverting the sheet S by reverse rotation; and a discharge portion 13 a onto which the sheet S with the image formed thereon is discharged.
- the sheet conveying portion 9 conveys the sheet S with the toner image formed by the image forming portion 14 .
- the sheet conveying portion 9 includes a sheet conveying path 15 a , a duplex conveying path 15 b , an oblique feed roller pair 16 , a U-turn roller pair 17 , a paper feed frame 20 , a guide frame 28 , a conveying roller pair 18 , 19 as a conveying portion, and a sheet detection portion 22 .
- the sheet conveying path 15 a is a conveying path for conveying the sheet S fed from the sheet feeding portion 8 and the sheet S conveyed from the duplex conveying path 15 b , and the toner image formed by the image forming portion 14 is transferred in a predetermined position therein.
- the duplex conveying path 15 b is a conveying path for re-conveying the sheet S inverted by the discharging roller pair 11 , 12 to the sheet conveying path 15 a for duplex printing.
- the oblique feed roller pair 16 is arranged along the duplex conveying path 15 b to convey the inverted sheet S.
- the U-turn roller pair 17 is arranged in the duplex conveying path 15 b to re-convey the sheet S conveyed through the duplex conveying path 15 b to the sheet conveying path 15 a.
- the paper feed frame 20 and the guide frame 28 are arranged near an upstream side of the image forming portion 14 along the sheet conveying path 15 a .
- the conveying roller pairs 18 , 19 are arranged on the sheet conveying path 15 a to convey the sheet S passing through the paper feed frame 20 and the guide frame 28 to the image forming portion 14 .
- the conveying roller pairs 18 , 19 includes a plurality of conveying rollers 19 and a plurality of conveying rotary members 18 facing the plurality of conveying rollers 19 .
- the conveying rollers 19 are fixed to a rotating shaft 19 a rotatably supported parallel to a rotating shaft direction of the photosensitive drums 1 a , 1 b , 1 c and 1 d , and rotate integrally with the rotating shaft 19 a .
- the conveying rotary members 18 are rotatably supported to the paper feed frame 20 .
- the conveying rotary members 18 are biased to the conveying rollers 19 by a conveying rotary member spring 21 attached to the paper feed frame 20 . This biasing force allows the conveying rotary members 18 to rotate following the conveying rollers 19 to convey the sheet S.
- the sheet detection portion 22 is arranged on a downstream side in the sheet conveying direction than the conveying roller pair 18 , 19 on the sheet conveying path 15 a .
- the sheet detection portion 22 detects a leading end position of the sheet S conveyed to the image forming portion 14 by the conveying roller pair 18 , 19 .
- the sheet S is fed from the sheet feeding portion 8 to the sheet conveying path 15 a and then conveyed by the conveying roller pair 18 , 19 to the image forming portion through the sheet detection portion 22 .
- the sheet detection portion 22 detects a leading end position of the sheet S.
- the image forming portion 14 starts to form a toner image.
- the sheet S passes through the transfer rollers 5 a , 5 b , 5 c and 5 d following the start of the toner image formation, the respective color toner images on the photosensitive drums 1 a , 1 b , 1 c and 1 d are sequentially transferred to the sheet S.
- the fixing portion 10 fixes unfixed toner images to the sheet S, and the sheet S is discharged by the discharging roller pair 11 , 12 to the discharge portion 13 a.
- the fixing portion 10 fixes the unfixed toner images to the sheet S, and then the discharging roller pair 11 , 12 reversely rotates before the sheet S is discharged by the discharging roller pair 11 , 12 to the discharge portion 13 a .
- the sheet S is conveyed to the duplex conveying path 15 b .
- the sheet S conveyed along the duplex conveying path 15 b passes through the sheet detection portion 22 by the oblique feed roller pair 16 and the U-turn roller pair 17 , and the sheet S is conveyed again to the image forming portion 14 to perform duplex printing.
- FIG. 2A is a perspective view illustrating the sheet detection portion 22 supported by the paper feed frame according to the first embodiment.
- FIG. 2B is a perspective view illustrating the sheet detection portion 22 viewed from an opposite side thereof illustrated in FIG. 2A .
- FIG. 3 is a perspective view illustrating a sensor flag 23 of the sheet detection portion 22 according to the first embodiment.
- the sheet detection portion 22 includes: a sensor flag 23 ; an optical sensor 24 as a sensor portion; a shutter driving portion 25 ; a shutter spring 27 as a biasing portion; and a rotation assist roller 30 as a rotation portion generating a driving force.
- an assist cam 23 c and the rotation assist roller 30 constitute a rotation transmission portion.
- the sensor flag 23 is supported by the paper feed frame 20 so as to be positioned on a downstream side of the conveying roller pair 18 , 19 near the image forming portion 14 .
- the sensor flag 23 includes: a shutter flag 23 a as a rotation detection portion; a light shielding portion 23 b as a rotation detection portion; the assist cam 23 c as a transmission portion; and a flag rotating shaft 23 d rotatably supported by the paper feed frame 20 .
- the flag rotating shaft 23 d is arranged parallel to the rotating shaft of the photosensitive drums 1 a , 1 b , 1 c and 1 d , rotatably supported by the paper feed frame 20 , and located on a downstream side of the conveying roller pair 18 , 19 .
- the shutter flag 23 a is fixed to the flag rotating shaft 23 d , and rotates integrally with the flag rotating shaft 23 d around the flag rotating shaft 23 d .
- the shutter flag 23 a has an abutting portion 23 e which is located on a downstream side of the conveying roller pair 18 , 19 , extends toward a nip portion of the conveying roller pair 18 , 19 and can abut against the leading end of the sheet S to be conveyed by the conveying roller pair 18 , 19 (see FIGS. 2A and 2B ).
- the abutting portion 23 e has an abutment surface 23 f abutting against the leading end of the sheet S to be conveyed from the conveying roller pair 18 , 19 .
- the light shielding portion 23 b shields an optical path L of the optical sensor.
- the light shielding portion 23 b is fixed to the flag rotating shaft 23 d and rotates integrally with the flag rotating shaft 23 d around the flag rotating shaft 23 d .
- the light shielding portion 23 b has a slit portion 23 g allowing passage of light from the optical sensor 24 .
- the slit portion 23 g is formed so as to allow passage of light from the optical sensor 24 when the abutment surface 23 f of the abutting portion 23 e provided in the shutter flag 23 a is positioned at a waiting position (hereinafter also referred to as a “home position”) of abutting against the sheet S (see FIG. 4D described later).
- the light shielding portion 23 b shields the optical path L of the optical sensor 24 .
- the position of the sensor flag 23 in which the abutment surface 23 f of the abutting portion 23 e is positioned at the home position so as to cause the leading end of the sheet S to abut against the abutment surface 23 f is referred to as a standby position of the sensor flag 23 .
- the urging force of the shutter spring 27 acts to maintain that the sensor flag 23 is located in the home position.
- the assist cam 23 c is fixed to the flag rotating shaft 23 d and rotates integrally with the flag rotating shaft 23 d around the flag rotating shaft 23 d . Further, the assist cam 23 c has an engaging portion 23 h engageable with the rotation assist roller 30 .
- the engaging portion 23 h engages with the rotation assist roller 30 after the abutment surface 23 f of the shutter flag 23 a is pushed by the sheet S to rotate up to a predetermined rotational position until a drive projection portion 25 b (described later) of the shutter driving portion 25 rotates over the top dead center.
- the predetermined rotational position refers to a rotational position at which rotation of the shutter flag 23 a causes rotation of the light shielding portion 23 b , causing the optical path L of the optical sensor 24 to be shielded by the light shielding portion 23 b.
- the optical sensor 24 is arranged in a rotation path of the light shielding portion 23 b .
- the optical sensor 24 includes a light emitting portion emitting light; and a light receiving portion receiving the light emitted from the light emitting portion. The light emitted from the light emitting portion is received by the light receiving portion to form the optical path L.
- a signal (light signal) output from the light emitting portion is shielded, and the received signal changes.
- the shutter driving portion 25 is connected to an end portion of the flag rotating shaft 23 d .
- the shutter driving portion 25 includes a disc-shaped drive base portion 25 a , and the drive projection portion 25 b to which one end of the shutter spring 27 is attached.
- the drive base portion 25 a is connected to the flag rotating shaft 23 d such that the central axis matches the flag rotating shaft 23 d .
- the drive base portion 25 a rotates with the flag rotating shaft 23 d .
- the drive projection portion 25 b is attached to an upper surface of the drive base portion 25 a such that the drive projection portion 25 b rotates along an outer periphery of the drive base portion 25 a around the flag rotating shaft 23 d when rotation of the flag rotating shaft 23 d rotates the drive base portion 25 a .
- the drive projection portion 25 b is attached to the drive base portion 25 a such that the abutment surface 23 f of the shutter flag 23 a is positioned at the home position at the bottom dead center.
- the shutter spring 27 biases the drive projection portion 25 b such that the abutment surface 23 f of the shutter flag 23 a is positioned at the home position. Specifically, the shutter spring 27 biases the drive projection portion 25 b such that the abutting portion 23 e of the shutter flag 23 a is positioned at the home position at the bottom dead center of the drive projection portion 25 b , that is, the sensor flag 23 is positioned at the standby position.
- the rotation assist roller 30 is arranged parallel to the rotating shaft direction of the photosensitive drums 1 a , 1 b , 1 c and 1 d and is rotatably supported by the paper feed frame 20 . Further, the rotation assist roller 30 is rotated by an not-illustrated drive portion (motor) in a direction indicated by an arrow r as illustrated in FIG. 2A .
- FIG. 4A illustrates the sheet detection portion 22 according to the first embodiment.
- FIG. 4B illustrates the assist cam 23 c and the rotation assist roller 30 in a state illustrated in FIG. 4A .
- FIG. 4C illustrates the abutting portion 23 e of the shutter flag 23 a in a state illustrated in FIG. 4A .
- FIG. 4D illustrates the light shielding portion 23 b in a state illustrated in FIG. 4A .
- FIG. 5A illustrates a state in which the sheet S abuts against the shutter flag 23 a .
- FIG. 5B illustrates the assist cam 23 c and the rotation assist roller 30 in a state illustrated in FIG. 5A .
- FIG. 5A illustrates the sheet detection portion 22 according to the first embodiment.
- FIG. 4B illustrates the assist cam 23 c and the rotation assist roller 30 in a state illustrated in FIG. 4A .
- FIG. 4C illustrates the abutting portion 23 e of the shutter flag 23 a in a state illustrated
- FIG. 5C illustrates the abutting portion 23 e of the shutter flag 23 a in a state illustrated in FIG. 5A .
- FIG. 5D illustrates the light shielding portion 23 b in a state illustrated in FIG. 5A .
- FIG. 6A illustrates a state in which the sensor flag 23 rotates to shield the optical path L of the optical sensor 24 .
- FIG. 6B illustrates the assist cam 23 c and the rotation assist roller 30 in a state illustrated in FIG. 6A .
- FIG. 6C illustrates the shutter flag 23 a in a state illustrated in FIG. 6A .
- FIG. 6D illustrates the light shielding portion 23 b in a state illustrated in FIG. 6A .
- FIG. 7A illustrates a state in which the assist cam 23 c engages with the rotation assist roller 30 .
- FIG. 7B illustrates the assist cam 23 c and the rotation assist roller 30 in a state illustrated in FIG. 7A .
- FIG. 7C illustrates the shutter flag 23 a in a state illustrated in FIG. 7A .
- FIG. 7D illustrates the light shielding portion 23 b in a state illustrated in FIG. 7A .
- FIG. 8A illustrates a state in which the assist cam 23 c is disengaged from the rotation assist roller 30 .
- FIG. 8B illustrates the assist cam 23 c and the rotation assist roller 30 in a state illustrated in FIG. 8A .
- FIG. 8C illustrates the shutter flag 23 a in a state illustrated in FIG. 8A .
- FIG. 8D illustrates the light shielding portion 23 b in a state illustrated in FIG. 8A .
- FIG. 9A illustrates a state in which the abutting portion 23 e of the shutter flag 23 a abuts against the sheet S and enters a wait state.
- FIG. 9B illustrates the assist cam 23 c and the rotation assist roller 30 in a state illustrated in FIG. 9A .
- FIG. 9C illustrates the shutter flag 23 a in a state illustrated in FIG. 9A .
- FIG. 9D illustrates the light shielding portion 23 b in a state illustrated in FIG. 9A .
- FIG. 10A illustrates a state in which the trailing end of the sheet S passes through the shutter flag 23 a .
- FIG. 10B illustrates the assist cam 23 c and the rotation assist roller 30 in a state illustrated in FIG. 10A .
- FIG. 10C illustrates the shutter flag 23 a in a state illustrated in FIG. 10A .
- FIG. 10D illustrates the light shielding portion 23 b in a state illustrated in FIG. 10A .
- the biasing force of the shutter spring 27 causes the abutting portion 23 e of the shutter flag 23 a to be held in a wait state at the home position.
- the assist cam 23 c is spaced apart from the rotation assist roller 30 , and the rotational driving force of the rotation assist roller 30 is not transmitted to the engaging portion 23 h of the assist cam 23 c .
- the optical path L of the optical sensor 24 is allowed to pass through the slit portion 23 g of the light shielding portion 23 b.
- the conveying force of the conveying roller pair 18 , 19 causes the sheet S to be conveyed.
- the abutment surface 23 f of the shutter flag 23 a is pushed by the leading end of the sheet S, the sheet S rotates the shutter flag 23 a in a direction indicated by an arrow z as illustrated in FIG. 5A .
- the sheet S is conveyed against the holding force of the shutter driving portion 25 biased by the shutter spring 27 .
- the leading end of the sheet S is guided by a paper feed guide including the paper feed frame 20 and the guide frame 28 and arranged downstream in the sheet conveying direction of the conveying roller pair 18 , 19 . Consequently, as illustrated in FIG.
- the paper feed guide can prevent the leading end of the sheet S from moving away from the abutment surface 23 f and allows the leading end of the sheet S to surely push and rotate the shutter flag 23 a .
- the assist cam 23 c is spaced apart from the rotation assist roller 30 , and the rotational driving force of the rotation assist roller 30 is not transmitted to the engaging portion 23 h of the assist cam 23 c.
- the abutment surface 23 f is pushed by the leading end of the sheet S and the shutter flag 23 a rotates against the biasing force of the shutter spring 27 .
- the optical path L of the optical sensor 24 is shielded by the light shielding portion 23 b .
- the sheet detection portion 22 detects that the shutter flag 23 a rotates up to a predetermined rotational position and the leading end of the sheet S is conveyed up to a desired position. Then, the sheet detection portion 22 sends a predetermined signal to the image forming portion 14 .
- the image forming portion 14 starts to form a toner image.
- the assist cam 23 c is spaced apart from the rotation assist roller 30 , and the rotational driving force of the rotation assist roller 30 is not transmitted to the engaging portion 23 h of the assist cam 23 c.
- the force for rotating the sensor flag 23 is switched from the conveying force of the sheet S to the rotational driving force of the rotation assist roller 30 , the state of which continues up to the state in which the drive projection portion 25 b of the shutter driving portion 25 exceeds the top dead center.
- the rotation of the assist cam 23 c rotates the sensor flag 23 in the same direction (as the direction indicated by an arrow z), causing the abutting portion 23 e (abutment surface 23 f ) of the shutter flag 23 a to retract from the sheet S.
- the optical path L of the optical sensor 24 is shielded by the light shielding portion 23 b.
- the drive projection portion 25 b of the shutter driving portion 25 reaches the top dead center.
- the engaging portion 23 h of the assist cam 23 c becomes spaced apart from the rotation assist roller 30 .
- the subsequent rotation of the sensor flag 23 is performed by the biasing force of the shutter spring 27 .
- FIGS. 8C and 8D also in this state, the optical path L of the optical sensor 24 is shielded by the light shielding portion 23 b.
- the sensor flag 23 is rotated by the biasing force of the shutter spring 27 in a direction indicated by an arrow z as illustrated in FIG. 8A . Then, as illustrated in FIGS. 9A and 9B , the abutting portion 23 e of the shutter flag 23 a abuts against the surface of the sheet S conveyed by the conveying roller pair 18 , 19 . At this time, the biasing force of the shutter spring 27 biases the sensor flag 23 to return the sensor flag 23 to the standby position, but the sensor flag 23 cannot return to the standby position because the sheet S being conveyed is positioned on the rotation path. As illustrated in FIG.
- the state (position) in which rotation is limited by abutting against the surface of the sheet S during passage is referred to as a sheet passing position of the sensor flag 23 .
- the optical path L of the optical sensor 24 is shielded by the light shielding portion 23 b.
- the shutter flag 23 a rotates in a direction indicated by an arrow z by the biasing force of the shutter spring 27 .
- the light shielding portion 23 b is released from shielding of the optical path L of the optical sensor 24 .
- the optical sensor 24 generates a transmission signal.
- the sensor flag 23 When the trailing end of the sheet S moves further away from the shutter flag 23 a as illustrated in FIGS. 10A to 10D , the sensor flag 23 is rotated by a rotational force generated by the shutter spring 27 and the shutter driving portion 25 . Then, the sensor flag 23 enters a wait state at the standby position for the abutment surface 23 f of the shutter flag 23 a to abut against the subsequent sheet S as illustrated in FIG. 4 .
- the image forming apparatus 100 according to the first embodiment having the above configuration can exert the following effects.
- the sheet detection portion 22 according to the first embodiment is configured such that the sensor flag 23 rotates in one direction and returns to the standby position by receiving a rotational driving force from the rotation assist roller 30 , the assist cam 23 c , and the shutter spring 27 constituting the rotation transmission portion.
- the sensor flag 23 rotates to enter a wait state of being in contact with a sheet near the standby position.
- the sensor flag 23 moves to the standby position. Consequently, the sensor flag can return to the standby position in a shorter time than the sensor flag takes to reciprocate.
- an increase in sheet gap distance can be prevented when increasing the conveying speed of the sheet S. More specifically, the sensor flag 23 can return to the standby position in a short sheet gap, which has been conventionally difficult under high sheet conveying speed conditions. As a result, throughput can be improved.
- the first embodiment can shorten the sheet gap to about half in comparison with a conventional sensor flag performing a reciprocating movement.
- the first embodiment can meet user demands to further improve throughput of the image forming apparatus.
- the assist cam 23 c assists rotation to prevent a biasing force from being applied to the leading end of the sheet after skew correction, thus preventing damage such as scratching and folding from occurring in the leading end of the sheet.
- the assist cam 23 c and the rotation assist roller 30 are used to transmit a rotational driving force to the sensor flag 23 and the biasing force of the shutter spring 27 is used to return the sensor flag 23 to the home position. Consequently, the rotational driving force can be transmitted to the sensor flag by a simple configuration. Thus, manufacturing costs can be suppressed or manufacturing at a low price is enabled.
- FIG. 11 is a perspective view illustrating a sheet detection portion 22 A supported by a paper feed frame 20 according to the second embodiment.
- FIG. 12 is a perspective view illustrating a sensor flag 23 A of the sheet detection portion 22 A according to the second embodiment.
- FIG. 13A illustrates the sheet detection portion 22 A according to the second embodiment.
- FIG. 13B illustrates an assist cam 23 c and a rotation assist roller 30 in a state illustrated in FIG. 13A .
- FIG. 13C illustrates an abutting portion 223 e of a shutter flag 223 a in a state illustrated in FIG. 13A .
- FIG. 13D illustrates a light shielding portion 23 b in a state illustrated in FIG. 13A .
- FIG. 14A illustrates a state in which the abutting portion 223 e of the shutter flag 223 a abuts against a sheet S and enters a wait state.
- FIG. 14B illustrates the assist cam 23 c and the rotation assist roller 30 in a state illustrated in FIG. 14A .
- FIG. 14C illustrates the shutter flag 223 a in a state illustrated in FIG. 14A .
- FIG. 14D illustrates the light shielding portion 23 b in a state illustrated in FIG. 14A .
- the second embodiment is different from the first embodiment in that the sheet detection portion 22 A of the second embodiment has a flag rotary member 223 k on a tip of an abutting portion 223 e of a shutter flag 223 a .
- the description of the second embodiment will focus on the difference from the first embodiment, namely, the flag rotary member 223 k provided on the shutter flag 223 a .
- the same reference numerals or characters are assigned to the same components as those of the image forming apparatus 100 according to the first embodiment and the description thereof is omitted.
- the same components as those of the first embodiment exert the same effects as those of the first embodiment.
- the image forming apparatus 100 A according to the second embodiment includes a sheet feeding portion 8 , an image forming portion 14 , a fixing portion 10 , a sheet conveying portion 9 A, and a sheet discharging portion 13 .
- the sheet conveying portion 9 A includes a sheet conveying path 15 a , a duplex conveying path 15 b , an oblique feed roller pair 16 , a U-turn roller pair 17 , the paper feed frame 20 , a guide frame 28 , a conveying roller pair 18 , 19 , and the sheet detection portion 22 A.
- the sheet detection portion 22 A includes the sensor flag 23 A, an optical sensor 24 , a shutter driving portion 25 , a shutter spring 27 , and the rotation assist roller 30 .
- the sensor flag 23 A includes the shutter flag 223 a , the light shielding portion 23 b , the assist cam 23 c , and a flag rotating shaft 23 d.
- the shutter flag 223 a includes the abutting portion 223 e , and the flag rotary member 223 k rotatably supported on the tip of the abutting portion 223 e .
- the flag rotary member 223 k is supported by the abutting portion 223 e so as to rotate while abutting against the surface of the sheet S to be conveyed.
- FIGS. 13A to 14D the operation of the sheet detection portion 22 A will be described.
- the abutting portion 223 e of the shutter flag 223 a is held in a wait state at the home position by the biasing force of the shutter spring 27 .
- the assist cam 23 c is spaced apart from the rotation assist roller 30 , and the rotational driving force of the rotation assist roller 30 is not transmitted to the engaging portion 23 h of the assist cam 23 c .
- an optical path L of the optical sensor 24 is allowed to pass through a slit portion 23 g of the light shielding portion 23 b.
- the image forming apparatus 100 A according to the second embodiment having the above configuration can exert not only the effects resulting from the same configuration as that of the first embodiment but also the following effects.
- the sheet detection portion 22 A according to the second embodiment has the flag rotary member 223 k on the tip of the abutting portion 223 e of the shutter flag 223 a . Consequently, even in a state in which the sensor flag 23 rotates and contacts the surface of the sheet S to enter a wait state, the flag rotary member 223 k rolls on and contacts the sheet S, thus preventing the abutting portion 223 e from contacting the sheet S in a scratching manner. Thus, a contact trace of the abutting portion 223 e is unlikely to remain to the sheet S.
- a larger effect can be expected in a case in which the conveying roller pair 18 , 19 is arranged downstream of the fixing apparatus and the abutting portion 223 e of the shutter flag 223 a contacts a toner image surface after the toner image is fixed.
- FIG. 15 is a perspective view illustrating a sheet detection portion 22 B supported by a paper feed frame 20 according to the third embodiment.
- FIG. 16 is a perspective view illustrating a sensor flag 23 B of the sheet detection portion 22 B according to the third embodiment.
- FIG. 17A illustrates the sheet detection portion 22 B according to the third embodiment.
- FIG. 17B illustrates a sensor cam 323 i , a shutter spring 327 , a cam follower 336 , and a pressing member 335 in a state illustrated in FIG. 17A .
- FIG. 17C illustrates an abutting portion 323 a and a light shielding portion 323 b of a shutter flag 323 in a state illustrated in FIG. 17A .
- FIG. 18A illustrates a state in which the sensor flag 23 B rotates to shield an optical path of an optical sensor.
- FIG. 18B illustrates the sensor cam 323 i , the shutter spring 327 , the cam follower 336 , and the pressing member in a state illustrated in FIG. 18A .
- FIG. 18C illustrates the abutting portion 323 a of the shutter flag 323 and the light shielding portion 323 b in a state illustrated in FIG. 18A .
- FIG. 19A illustrates a state in which the sensor cam 323 i engages with a rotation assist roller 30 .
- FIG. 19B illustrates the sensor cam 323 i , the shutter spring 327 , the cam follower 336 , and the pressing member 335 in a state illustrated in FIG. 19A .
- FIG. 19C illustrates the abutting portion 323 a and the light shielding portion 323 b of the shutter flag 323 in a state illustrated in FIG. 19A .
- FIG. 20A illustrates a state in which the sensor cam 323 i disengages from the rotation assist roller 30 .
- FIG. 20B illustrates the sensor cam, the shutter spring 327 , the cam follower 336 , and the pressing member 335 in a state illustrated in FIG. 20A .
- FIG. 20C illustrates the abutting portion 323 a and the light shielding portion 323 b of the shutter flag 323 in a state illustrated in FIG. 20A .
- FIG. 21A illustrates a state in which the abutting portion 323 a of the shutter flag 323 abuts against the sheet and enters a wait state.
- FIG. 21B illustrates the sensor cam 323 i , the shutter spring 327 , the cam follower 336 , and the pressing member 335 in a state illustrated in FIG. 21A .
- FIG. 21C illustrates the abutting portion 323 a and the light shielding portion 323 b of the shutter flag 323 in a state illustrated in FIG. 21A .
- FIG. 22A illustrates a state in which the trailing end of a sheet S passes through the shutter flag 323 .
- FIG. 22B illustrates the sensor cam 323 i , the shutter spring 327 , the cam follower 336 , and the pressing member 335 in a state illustrated in FIG. 22A .
- FIG. 22C illustrates the abutting portion 323 a and the light shielding portion 323 b of the shutter flag 323 in a state illustrated in FIG. 22A .
- the third embodiment is different from the first embodiment in that the image forming apparatus 100 B according to the third embodiment provides the sensor cam 323 i , the shutter spring 327 , the pressing member 335 , and the cam follower 336 to exert a biasing force to bias the shutter flag 223 . Further, the third embodiment is different from the first embodiment in the shape of the sensor flag 23 B. Thus, the description of the third embodiment will focus on the differences from the first embodiment.
- the same reference numerals or characters are assigned to the same components as those of the image forming apparatus 100 according to the first embodiment and the description thereof is omitted. That is, in the third embodiment, the same components as those of the first embodiment exert the same effects as those of the first embodiment.
- the image forming apparatus 100 B according to the third embodiment includes a sheet feeding portion 8 , an image forming portion 14 , a fixing portion 10 , a sheet conveying portion 9 B, and a sheet discharging portion 13 .
- the sheet conveying portion 9 B includes a sheet conveying path 15 a , a duplex conveying path 15 b , an oblique feed roller pair 16 , a U-turn roller pair 17 , the paper feed frame 20 , a guide frame 28 , a conveying roller pair 18 , 19 , and the sheet detection portion 22 B.
- the sheet detection portion 22 B includes the sensor flag 23 B, an optical sensor 24 , the shutter spring 327 , the pressing member 335 , the cam follower 336 , and the rotation assist roller 30 .
- the sensor flag 23 B includes the shutter flag 323 , the light shielding portion 323 b , an assist cam 323 c , the sensor cam 323 i , and a flag rotating shaft 23 d.
- the shutter flag 323 includes the abutting portion 323 a and the light shielding portion 323 b .
- the abutting portion 323 a includes an abutting portion 323 a 1 , an abutting portion 323 a 2 , and an abutting portion 323 a 3 .
- the light shielding portion 323 b includes a light shielding portion 323 b 1 , a light shielding portion 323 b 2 , and a light shielding portion 323 b 3 .
- the assist cam 323 c includes an engaging portion 323 c 1 , an engaging portion 323 c 2 , and an engaging portion 323 c 3 to engage with the rotation assist roller 30 .
- the sensor cam 323 i is fixed to the flag rotating shaft 23 d and rotates integrally with the flag rotating shaft 23 d .
- the sensor cam 323 i uses the shutter spring 327 , the cam follower 336 , and the pressing member 335 to exert a biasing force to bias the sensor flag 23 B.
- the operation of the sheet detection portion 22 B will be described.
- the abutting portion 323 a of the shutter flag 323 is held in a wait state at the home position by the biasing force of the shutter spring 27 .
- the assist cam 323 c is spaced apart from the rotation assist roller 30 , and the rotational driving force of the rotation assist roller 30 is not transmitted to any of the engaging portion 323 c 1 , the engaging portion 323 c 2 , and the engaging portion 323 c 3 of the assist cam 323 c .
- an optical path L of the optical sensor 24 enters a state of not being shielded by any of the light shielding portion 323 b 1 , the light shielding portion 323 b 2 , and the light shielding portion 323 b 3 of the shutter flag 323 .
- the sheet detection portion 22 B detects that the shutter flag 323 rotates up to a predetermined rotational position and the leading end of the sheet S is conveyed up to a desired position. Then, the sheet detection portion 22 B sends a predetermined signal to the image forming portion 14 .
- the image forming portion 14 starts to form a toner image.
- the assist cam 323 c is spaced apart from the rotation assist roller 30 , and the rotational driving force of the rotation assist roller 30 is not transmitted to the engaging portion 323 c 1 of the assist cam 323 c.
- the shutter flag 323 is further rotated by the leading end of the sheet S, the engaging portion 323 c 1 of the assist cam 323 c engages with the rotation assist roller 30 rotating in a direction indicated by an arrow r.
- the engaging portion 323 c 1 of the assist cam 323 c engages with the rotation assist roller 30
- the rotational driving force of the rotation assist roller 30 is transmitted to the engaging portion 323 c 1 and the assist cam 323 c rotates in a direction indicated by an arrow z.
- the force for rotating the sensor flag 23 B is switched from the conveying force of the sheet S to the rotational driving force of the rotation assist roller 30 .
- the rotation continues up to the state in which the sensor cam 323 i exceeds the top dead center.
- the rotation of the assist cam 323 c rotates the shutter flag 323 in the same direction (as the direction indicated by an arrow z), causing the abutting portion 323 a 1 of the shutter flag 323 to retract from the sheet S.
- the optical path L of the optical sensor 24 is shielded by the light shielding portion 323 b 2 .
- the sensor cam 323 i also rotates in a direction indicated by an arrow z, and thus the sensor cam 323 i assists in pushing down the cam follower 336 , the pressing member 335 , and the shutter spring 327 .
- the sensor cam 323 i reaches the top dead center.
- the engaging portion 323 c 1 of the assist cam 323 c becomes spaced apart from the rotation assist roller 30 .
- the biasing force of the cam follower 336 , the pressing member 335 , and the shutter spring 327 pushes up the sensor cam 323 i to rotate the shutter flag 323 .
- the optical path L of the optical sensor 24 is shielded by the light shielding portion 323 b 2 .
- the abutting portion 323 a 2 of the shutter flag 323 enters a state of being biased by the shutter spring 327 and the like to abut against the surface of the sheet S in a wait state.
- the optical path L of the optical sensor 24 is also shielded by the light shielding portion 323 b 2 .
- the shutter flag 323 rotates in a direction indicated by an arrow z as illustrated in FIGS. 22A to 22C .
- the light shielding portion 323 b 2 is released from shielding of the optical path L of the optical sensor 24 as illustrated in FIG. 22C .
- the optical sensor 24 generates a transmission signal.
- the trailing end of the sheet S can be detected.
- the sensor flag 23 B When the trailing end of the sheet S moves away from the shutter flag 323 as illustrated in FIGS. 22A to 22C , the sensor flag 23 B is rotated by a rotational force generated by the shutter spring 327 , the sensor cam 323 i , and the like. Then, the sensor flag 23 B enters a wait state at the home position for the abutting portion 323 a 2 of the shutter flag 323 to abut against a leading end of the subsequent sheet S as illustrated in FIG. 17A .
- the image forming apparatus 100 B according to the third embodiment having the above configuration can exert not only the effects resulting from the same configuration as that of the first embodiment but also the following effects.
- the sheet detection portion 22 B according to the third embodiment includes the shutter flag 323 having the abutting portions 323 a 1 , 323 a 2 and 323 a 3 , and the light shielding portions 323 b 1 , 323 b 2 and 323 b 3 ; the assist cam 323 c having the engaging portions 323 c 1 , 323 c 2 and 323 c 3 ; and the sensor cam 323 i . Accordingly, the sheet detection portion 22 B can detect the leading end of the sheet S without a whole turn of the sensor flag 23 B. Thus, it can take less time to position the abutting portion 323 a at the home position, and an increase in sheet gap distance can be prevented when increasing the conveying speed of the sheet S. As a result, throughput can be improved.
- the sheet detection portion 22 B of the third embodiment even the configuration of biasing the shutter flag 323 by using the shutter spring 327 and the assist cam 323 c can assist the shutter flag 323 in giving the sensor cam 323 i a force for rolling over the top dead center.
- Use of the assist cam 323 c to assist the rotation can eliminate the need for the force for pushing the shutter flag 323 to depend only on stiffness of the sheet S, thus preventing damage such as scratching and folding from occurring in the leading end of the sheet S.
- FIG. 23A is a perspective view illustrating a sheet detection portion 22 C supported by a paper feed frame according to the fourth embodiment.
- FIG. 23B is a perspective view illustrating the sheet detection portion 22 C viewed from an opposite side thereof illustrated in FIG. 23A .
- FIG. 24A illustrates the sheet detection portion 22 C according to the fourth embodiment.
- FIG. 24B illustrates an assist gear and a rotation assist gear in a state illustrated in FIG. 24A .
- FIG. 24C illustrates an abutting portion 23 e of a shutter flag in a state illustrated in FIG. 24A .
- FIG. 24D illustrates a light shielding portion in a state illustrated in FIG. 24A .
- FIG. 25A illustrates a state in which the assist gear engages with the rotation assist gear.
- FIG. 25B illustrates the assist gear and the rotation assist gear in a state illustrated in FIG. 25A .
- FIG. 25C illustrates the shutter flag in a state illustrated in FIG. 25A .
- FIG. 25D illustrates the light shielding portion in a state illustrated in FIG. 25A .
- FIG. 26A illustrates a state in which the abutting portion 23 e of the shutter flag abuts against a sheet and enters a wait state.
- FIG. 26B illustrates the assist gear and the rotation assist gear in a state illustrated in FIG. 26A .
- FIG. 26C illustrates the shutter flag in a state illustrated in FIG. 26A .
- FIG. 26D illustrates the light shielding portion in a state illustrated in FIG. 26A .
- the fourth embodiment is different from the first embodiment in that the image forming apparatus 100 C of the fourth embodiment uses an assist gear 423 c and a rotation assist gear 430 .
- the description of the fourth embodiment will focus on the difference from the first embodiment, namely, the assist gear 423 c and the rotation assist gear 430 .
- the same reference numerals or characters are assigned to the same components as those of the image forming apparatus 100 according to the first embodiment and the description thereof is omitted.
- the same components as those of the first embodiment exert the same effects as those of the first embodiment.
- the image forming apparatus 100 C according to the fourth embodiment includes a sheet feeding portion 8 , an image forming portion 14 , a fixing portion 10 , a sheet conveying portion 9 C, and a sheet discharging portion 13 .
- the sheet conveying portion 9 C includes a sheet conveying path 15 a , a duplex conveying path 15 b , an oblique feed roller pair 16 , a U-turn roller pair 17 , the paper feed frame 20 , a guide frame 28 , a conveying roller pair 18 , 19 , and the sheet detection portion 22 C.
- the sheet detection portion 22 C includes a sensor flag 23 C, an optical sensor 24 , a shutter driving portion 25 , a shutter spring 27 , and the rotation assist gear 430 as a rotation portion.
- the sensor flag 23 C includes a shutter flag 23 a , a light shielding portion 23 b , the assist gear 423 c , and a flag rotating shaft 23 d.
- the rotation assist gear 430 is formed into a gear shape whose outer peripheral surface has a plurality of teeth.
- the assist gear 423 c is arranged in a predetermined range of the outer peripheral surface thereof and includes an interrupted toothed portion 423 h as an interrupted toothed gear meshing with the rotation assist gear 430 .
- the interrupted toothed portion 423 h engages with the rotation assist gear 430 until a drive projection portion 25 b of the shutter driving portion 25 rotates and exceeds the top dead center.
- FIGS. 24A to 26D the operation of the sheet detection portion 22 C will be described.
- the abutting portion 23 e of the shutter flag 23 a is held in a wait state at the home position by the biasing force of the shutter spring 27 .
- FIG. 24A and 24C in a state in which the leading end of the sheet S does not abut against the abutment surface 23 f of the shutter flag 23 a , the abutting portion 23 e of the shutter flag 23 a is held in a wait state at the home position by the biasing force of the shutter spring 27 .
- the interrupted toothed portion 423 h of the assist gear 423 c is spaced apart from the rotation assist gear 430 , and the rotational driving force of the rotation assist gear 430 is not transmitted to the interrupted toothed portion 423 h of the assist gear 423 c .
- an optical path L of the optical sensor 24 is allowed to pass through a slit portion 23 g of the light shielding portion 23 b.
- the force for rotating the sensor flag 23 C is switched from the conveying force of the sheet S to the rotational driving force of the rotation assist gear 430 , the state of which continues up to the state in which the drive projection portion 25 b of the shutter driving portion 25 exceeds the top dead center.
- the rotation of the assist gear 423 c rotates the sensor flag 23 C in the same direction (as the direction indicated by an arrow z), causing the abutting portion 23 e (abutment surface 23 f ) of the shutter flag 23 a to retract from the sheet S.
- the optical path L of the optical sensor 24 is shielded by the light shielding portion 23 b.
- the interrupted toothed portion 423 h of the assist gear 423 c becomes spaced apart from the rotation assist gear 430 .
- the subsequent rotation of the sensor flag 23 C is performed by the biasing force of the shutter spring 27 .
- the sensor flag 23 C rotates in a direction indicated by an arrow z by the biasing force of the shutter spring 27 , as illustrated in FIGS. 26A and 26B , the abutting portion 23 e of the shutter flag 23 a abuts against the surface of the sheet S conveyed by the conveying roller pair 18 , 19 .
- the biasing force of the shutter spring 27 biases the shutter flag 23 a to return the shutter flag 23 a to the home position, but the shutter flag 23 a cannot return to the home position until the sheet S passes therethrough because the sheet S is conveyed. Accordingly, as illustrated in FIG. 26C , in a state of being biased by the shutter spring 27 , the shutter flag 23 a abuts against the surface of the sheet S to enter a wait state. As illustrated in FIG. 26D , also in this state, the optical path L of the optical sensor 24 is shielded by the light shielding portion 23 b.
- the shutter flag 23 a rotates in a direction indicated by an arrow z.
- the light shielding portion 23 b is released from shielding of the optical path L of the optical sensor 24 .
- the optical sensor 24 generates a transmission signal.
- the sensor flag 23 C When the trailing end of the sheet S moves away from the shutter flag 23 a , the sensor flag 23 C is rotated by a rotational force generated by the shutter spring 27 and the shutter driving portion 25 . Then, the abutment surface 23 f of the shutter flag 23 a enters a wait state at the home position for detecting the subsequent sheet S as illustrated in FIG. 24A .
- the image forming apparatus 100 C according to the fourth embodiment having the above configuration can exert not only the effects resulting from the same configuration as that of the first embodiment but also the following effects.
- the sheet detection portion 22 C according to the fourth embodiment meshes the rotation assist gear 430 with the interrupted toothed portion 423 h of the assist gear 423 c to rotate the sensor flag 23 C. Accordingly, the fourth embodiment can suppress slippage due to wear of rollers and cams more than the configuration of engaging the rotation assist roller 30 with the assist cam 23 c . Thus, the fourth embodiment can assure more reliable meshing and can increase meshing reliability.
- FIG. 27 is a perspective view illustrating a sheet detection portion 22 D supported by a paper feed frame 20 according to the fifth embodiment.
- FIG. 28 is a perspective view illustrating a sensor flag 23 D of the sheet detection portion 22 D according to the fifth embodiment.
- FIG. 29 illustrates the sheet detection portion 22 D according to the fifth embodiment.
- the image forming apparatus 100 D of the fifth embodiment is different from the first embodiment in that a light shielding portion 23 b and a slit portion 23 g are provided on a shutter flag 123 a having an abutting portion 23 e .
- the description of the fifth embodiment will focus on the difference from the first embodiment, namely, the shutter flag 123 a .
- the same reference numerals or characters are assigned to the same components as those of the image forming apparatus 100 according to the first embodiment and the description thereof is omitted. That is, in the fifth embodiment, the same components as those of the first embodiment exert the same effects as those of the first embodiment.
- the image forming apparatus 100 D according to the fifth embodiment includes a sheet feeding portion 8 , an image forming portion 14 , a fixing portion 10 , a sheet conveying portion 9 D, and a sheet discharging portion 13 .
- the sheet conveying portion 9 D includes a sheet conveying path 15 a , a duplex conveying path 15 b , an oblique feed roller pair 16 , a U-turn roller pair 17 , the paper feed frame 20 , a guide frame 28 , a conveying roller pair 18 , 19 , and the sheet detection portion 22 D.
- the sheet detection portion 22 D includes the sensor flag 23 D, an optical sensor 24 , a shutter driving portion 25 , a shutter spring 27 , and a rotation assist roller 30 .
- the sensor flag 23 D includes the shutter flag 123 a , an assist cam 23 c , and a flag rotating shaft 23 d.
- the shutter flag 123 a includes the abutting portion 23 e which can abut against the leading end of a sheet S conveyed by the conveying roller pair 18 , 19 ; the light shielding portion 23 b as a rotation detection portion; and the slit portion 23 g passing light from the optical sensor 24 .
- the image forming apparatus 100 D according to the fifth embodiment having the above configuration can exert not only the effects resulting from the same configuration as that of the first embodiment but also the following effects.
- the shutter flag 123 a and the light shielding portion 23 b are made of the same member.
- the abutting portion 23 e , the light shielding portion 23 b and the slit portion 23 g are formed from the same member. Accordingly, when providing the shutter flag 123 a , costs can be reduced and space can be saved.
- the rotation assist roller 30 is arranged independently, but the present invention is not limited to this.
- the rotation assist roller 30 may be arranged on the rotating shaft 19 a of the conveying rollers 19 so as to face the assist cam 23 c integrally formed with the sensor flag 23 . This arrangement can reduce costs and save space more than the independent arrangement of the rotation assist roller 30 .
- the third embodiment describes that the sheet detection portion 22 B detects the sheet S, and the image is formed so as to be matched with the sheet based on the signal from the sheet detection portion 22 B, but the present invention is not limited to this.
- a configuration may be made such that first, the image formation is performed and after the sheet S is detected by the sheet detection portion 22 , the sheet is positioned to the image.
- the biasing force of the shutter spring 27 is used to return the sensor flag to the home position, but the present invention is not limited to this.
- a configuration may be made such that the sensor flag returns to the home position by adjusting the weight balance of the sensor flag or using gravitational force.
- the shutter spring 27 is mounted on the drive projection portion 25 b of the shutter driving portion 25 , but the present invention is not limited to this.
- the shutter spring 27 may be mounted on the assist gear 423 c.
Abstract
A sheet conveying apparatus including, a conveying portion conveying a sheet; a rotation detection portion rotatably provided; a sensor portion detecting the conveyed sheet based on a rotational position of the rotation detection portion; a rotation transmission portion transmitting a rotational driving force to the rotation detection portion to rotate the rotation detection portion in a predetermined rotational direction after the rotation detection portion is rotated by being pushed by the leading end of the sheet; and an urging unit configured to apply an urging force to the rotation detection portion so that the rotation detection portion comes into contact with a surface of the sheet, thereafter the rotation detection portion is returned to a waiting position along with the passage of the rear end of the sheet through the rotation detection portion after the rotation detection portion is rotated by the rotational driving force of the rotation transmitting unit.
Description
- 1. Field of the Invention
- The present invention relates to a sheet conveying apparatus and an image forming apparatus having the same, and more particularly to an image forming apparatus having a sheet conveying apparatus which can detect a leading end position of a sheet to be conveyed.
- 2. Description of the Related Art
- In general, the image forming apparatus provides a sheet conveying portion with a sheet detection portion detecting a leading end position of a sheet in order to match the time to send the sheet to an image transfer position with the time to send an image (toner image) to the image transfer position. The image forming apparatus provides the sheet conveying portion with a plurality of sheet detection portions to detect a sheet conveying state along a sheet conveying path such as a sheet conveyance delay and a jam (see Japanese Patent Application Laid-Open No. H09-183539).
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FIGS. 30 to 31B illustrate a conventionally general sheet detection portion. As illustrated inFIG. 30 , a conventional sheet detection portion includes asensor flag 523 and anoptical sensor 524. The sheet detection portion is arranged on a downstream side in a sheet conveying direction of a sheetconveying roller pairs sensor flag 523 includes a rotatingshaft 527 rotating thesensor flag 523; alight shielding portion 525 shielding an optical path L from a light emitting portion to a light receiving portion of theoptical sensor 524; astopper portion 526 positioning thesensor flag 523 to a home position; and areturn spring 528. Even if thesensor flag 523 rotates, thesensor flag 523 returns to the home position by its own weight or a pressing force of thereturn spring 528. - As illustrated in
FIG. 31A , when a leading end of a sheet S contacts thesensor flag 523, thesensor flag 523 rotates from the home position to a direction indicated by an arrow M1 around the rotatingshaft 527 and thelight shielding portion 525 shields the optical path L of theoptical sensor 524. When theoptical sensor 524 detects that the optical path L is shielded, the sheet detection device recognizes that the leading end of the sheet S reaches thesensor flag 523.FIG. 31B illustrates a state in which the sheet is passing through and in contact with thesensor flag 523. When a trailing end of the sheet S passes through thesensor flag 523, thesensor flag 523 returns to the home position illustrated inFIG. 31A . At this time, thelight shielding portion 525 retracts from the optical path L, allowing the light receiving portion of theoptical sensor 524 to receive light emitted from the light emitting portion again. Then, the sheet detection device recognizes that the trailing end of the sheet S has passed through thesensor flag 523. In recent years, the image forming apparatus has been required to meet user demand to further improve throughput. In order to improve throughput of the image forming apparatus, it is needed to increase a sheet conveying speed or shorten an interval from the trailing end of a preceding sheet to the leading end of a subsequent sheet (hereinafter referred to as a sheet gap). Consequently, the sheet detection device needs to return the sensor flag to the home position in a short sheet gap after the preceding sheet has passed - The
conventional sensor flag 523 operates such that when the leading end of the sheet S passed through the conveying roller pair abuts against an abutting portion, the sensor flag is pushed by the sheet S to rotate, and when the trailing end of the sheet moves away from the abutting portion, the sensor flag reversely rotates to return to a home position P. Consequently, the distance required for the sheet gap is a distance D3 obtained by adding a distance D1 from a position in which the trailing end of the preceding sheet passes through the abutting portion of the sensor flag to the home position P in which the leading end of the subsequent sheet abuts against the abutting portion to a distance D2 between which the subsequent sheet is conveyed (seeFIG. 31B ). - The distance D2 is a distance obtained by multiplying a time Δt during which the
sensor flag 523 moves across the distance D1 by a sheet conveying speed V (Δt×V). When thesensor flag 523 reciprocates, the distance D1 for thesensor flag 523 to return to the home position P is needed, and the higher the sheet conveying speed, the longer the distance D2 for the subsequent sheet to be conveyed during the return movement. Thus, the conventional sheet detection device has a problem in that an increase in the sheet conveying speed increases the sheet gap distance, which inhibits further improvement in throughput. - The present invention provides a sheet conveying apparatus inhibiting an increase in sheet gap distance while increasing a sheet conveying speed to improve throughput, and an image forming apparatus having the same.
- The present invention provides a sheet conveying apparatus including: a conveying portion configured to convey a sheet; a rotation detection portion rotatably provided and having an abutting portion which abuts against a leading end of the sheet conveyed by the conveying portion at a waiting position, wherein the rotation detection portion is rotated in a predetermined rotational direction by being pushed by the leading end of the conveyed sheet; a sensor portion detecting the conveyed sheet based on a rotational position of the rotation detection portion; a rotation transmission portion configured to transmit a rotational driving force to the rotation detection portion to rotate the rotation detection portion in the predetermined rotational direction after the rotation detection portion is rotated by being pushed by the leading end of the conveyed sheet; and an urging unit configured to apply an urging force to the rotation detection portion, wherein after the rotation detection portion is rotated by the rotational driving force of the rotation transmission portion, the urging unit applies the urging force to the rotation detection portion so that the rotation detection portion comes into contact with a surface of the sheet, thereafter the rotation detection portion is returned to the waiting position along with the passage of the rear end of the sheet through the rotation detection portion.
- The present invention can shorten the time needed from when the sheet passes to when the rotation detection portion is positioned in the standby position, thereby reducing the need to secure a long distance required for a sheet gap distance and thus improving throughput.
- Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
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FIG. 1 is a sectional view schematically illustrating an entire structure of an image forming apparatus according to a first embodiment of the present invention. -
FIG. 2A is a perspective view illustrating a sheet detection portion supported by a paper feed frame according to the first embodiment. -
FIG. 2B is a perspective view illustrating the sheet detection portion viewed from an opposite side thereof illustrated inFIG. 2A . -
FIG. 3 is a perspective view illustrating a sensor flag of the sheet detection portion according to the first embodiment. -
FIG. 4A illustrates the sheet detection portion according to the first embodiment. -
FIG. 4B illustrates an assist cam and a rotation assist roller in a state illustrated inFIG. 4A . -
FIG. 4C illustrates an abutting portion of a shutter flag in a state illustrated inFIG. 4A . -
FIG. 4D illustrates a light shielding portion in a state illustrated inFIG. 4A . -
FIG. 5A illustrates a state in which a sheet abuts against the sensor flag. -
FIG. 5B illustrates an assist cam and a rotation assist roller in a state illustrated inFIG. 5A . -
FIG. 5C illustrates the abutting portion of the shutter flag in a state illustrated inFIG. 5A . -
FIG. 5D illustrates the light shielding portion in a state illustrated inFIG. 5A . -
FIG. 6A illustrates a state in which the sensor flag rotates to shield an optical path of the optical sensor. -
FIG. 6B illustrates the assist cam and the rotation assist roller in a state illustrated inFIG. 6A . -
FIG. 6C illustrates the shutter flag in a state illustrated inFIG. 6A . -
FIG. 6D illustrates the light shielding portion in a state illustrated inFIG. 6A . -
FIG. 7A illustrates a state in which the assist cam engages with the rotation assist roller. -
FIG. 7B illustrates the assist cam and the rotation assist roller in a state illustrated inFIG. 7A . -
FIG. 7C illustrates the shutter flag in a state illustrated inFIG. 7A . -
FIG. 7D illustrates the light shielding portion in a state illustrated inFIG. 7A . -
FIG. 8A illustrates a state in which the assist cam disengages from the rotation assist roller. -
FIG. 8B illustrates the assist cam and the rotation assist roller in a state illustrated inFIG. 8A . -
FIG. 8C illustrates the shutter flag in a state illustrated inFIG. 8A . -
FIG. 8D illustrates the light shielding portion in a state illustrated inFIG. 8A . -
FIG. 9A illustrates a state in which the abutting portion of the shutter flag abuts against the sheet and enters a wait state. -
FIG. 9B illustrates the assist cam and the rotation assist roller in a state illustrated inFIG. 9A . -
FIG. 9C illustrates the shutter flag in a state illustrated inFIG. 9A . -
FIG. 9D illustrates the light shielding portion in a state illustrated inFIG. 9A . -
FIG. 10A illustrates a state in which the trailing end of the sheet passes through the shutter flag. -
FIG. 10B illustrates the assist cam and the rotation assist roller in a state illustrated inFIG. 10A . -
FIG. 10C illustrates the shutter flag in a state illustrated inFIG. 10A . -
FIG. 10D illustrates the light shielding portion in a state illustrated inFIG. 10A . -
FIG. 11 is a perspective view illustrating a sheet detection portion supported by a paper feed frame according to a second embodiment. -
FIG. 12 is a perspective view illustrating a sensor flag of the sheet detection portion according to the second embodiment. -
FIG. 13A illustrates the sheet detection portion according to the second embodiment. -
FIG. 13B illustrates an assist cam and a rotation assist roller in a state illustrated inFIG. 13A . -
FIG. 13C illustrates an abutting portion of a shutter flag in a state illustrated inFIG. 13A . -
FIG. 13D illustrates a light shielding portion in a state illustrated inFIG. 13A . -
FIG. 14A illustrates a state in which the abutting portion of the shutter flag abuts against a sheet and enters a wait state. -
FIG. 14B illustrates the assist cam and the rotation assist roller in a state illustrated inFIG. 14A . -
FIG. 14C illustrates the shutter flag in a state illustrated inFIG. 14A . -
FIG. 14D illustrates the light shielding portion in a state illustrated inFIG. 14A . -
FIG. 15 is a perspective view illustrating a sheet detection portion supported by a paper feed frame according to a third embodiment. -
FIG. 16 is a perspective view illustrating a sensor flag of the sheet detection portion according to the third embodiment. -
FIG. 17A illustrates the sheet detection portion according to the third embodiment. -
FIG. 17B illustrates a sensor cam, a shutter spring, a cam follower, and a pressing member in a state illustrated inFIG. 17A . -
FIG. 17C illustrates an abutting portion and a light shielding portion of a shutter flag in a state illustrated inFIG. 17A . -
FIG. 18A illustrates a state in which the sensor flag rotates to shield an optical path of an optical sensor. -
FIG. 18B illustrates the sensor cam, the shutter spring, the cam follower, and the pressing member in a state illustrated inFIG. 18A . -
FIG. 18C illustrates the abutting portion and the light shielding portion of the shutter flag in a state illustrated inFIG. 18A . -
FIG. 19A illustrates a state in which the sensor cam engages with a rotation assist roller. -
FIG. 19B illustrates the sensor cam, the shutter spring, the cam follower, and the pressing member in a state illustrated inFIG. 19A . -
FIG. 19C illustrates the abutting portion and the light shielding portion of the shutter flag in a state illustrated inFIG. 19A . -
FIG. 20A illustrates a state in which the sensor cam disengages from the rotation assist roller. -
FIG. 20B illustrates the sensor cam, the shutter spring, the cam follower, and the pressing member in a state illustrated inFIG. 20A . -
FIG. 20C illustrates the abutting portion and the light shielding portion of the shutter flag in a state illustrated inFIG. 20A . -
FIG. 21A illustrates a state in which the abutting portion of the shutter flag abuts against a sheet and enters a wait state. -
FIG. 21B illustrates the sensor cam, the shutter spring, the cam follower, and the pressing member in a state illustrated inFIG. 21A . -
FIG. 21C illustrates the abutting portion and the light shielding portion of the shutter flag in a state illustrated inFIG. 21A . -
FIG. 22A illustrates a state in which the trailing end of the sheet passes through the shutter flag. -
FIG. 22B illustrates the sensor cam, the shutter spring, the cam follower, and the pressing member in a state illustrated inFIG. 22A . -
FIG. 22C illustrates the abutting portion and the light shielding portion of the shutter flag in a state illustrated inFIG. 22A . -
FIG. 23A is a perspective view illustrating a sheet detection portion supported by a paper feed frame according to a fourth embodiment. -
FIG. 23B is a perspective view illustrating the sheet detection portion viewed from an opposite side thereof illustrated inFIG. 23A . -
FIG. 24A illustrates the sheet detection portion according to the fourth embodiment. -
FIG. 24B illustrates an assist gear and a rotation assist gear in a state illustrated inFIG. 24A . -
FIG. 24C illustrates an abutting portion of a shutter flag in a state illustrated inFIG. 24A . -
FIG. 24D illustrates a light shielding portion in a state illustrated inFIG. 24A . -
FIG. 25A illustrates a state in which the assist gear engages with the rotation assist gear. -
FIG. 25B illustrates the assist gear and the rotation assist gear in a state illustrated inFIG. 25A . -
FIG. 25C illustrates the shutter flag in a state illustrated inFIG. 25A . -
FIG. 25D illustrates the light shielding portion in a state illustrated inFIG. 25A . -
FIG. 26A illustrates a state in which the abutting portion of the shutter flag abuts against a sheet and enters a wait state. -
FIG. 26B illustrates the assist gear and the rotation assist gear in a state illustrated inFIG. 26A . -
FIG. 26C illustrates the shutter flag in a state illustrated inFIG. 26A . -
FIG. 26D illustrates the light shielding portion in a state illustrated inFIG. 26A . -
FIG. 27 is a perspective view illustrating a sheet detection portion supported by a paper feed frame according to a fifth embodiment. -
FIG. 28 is a perspective view illustrating a sensor flag of the sheet detection portion according to the fifth embodiment. -
FIG. 29 illustrates the sheet detection portion according to the fifth embodiment. -
FIG. 30 is a perspective view illustrating a sheet detection portion according to a conventional image forming apparatus. -
FIG. 31A illustrates an operation of a shutter flag according to the conventional sheet detection portion illustrated inFIG. 30 . -
FIG. 31B illustrates an operation of the shutter flag according to the conventional sheet detection portion illustrated inFIG. 30 . - Embodiments of the present invention will now be described in detail in accordance with the accompanying drawings.
- Now, an image forming apparatus having a sheet conveying apparatus according to embodiments of the present invention will be described referring to the accompanying drawings. The image forming apparatus according to the embodiments of the present invention is an image forming apparatus, such as a copier, a printer, a fax machine and a combined machine thereof, which has a sheet detection function of detecting a leading end of a sheet to be conveyed. The following embodiments will be described using an electrophotographic
image forming apparatus 100 forming a four-color toner image. - The
image forming apparatus 100 according to a first embodiment of the present invention will be described referring toFIGS. 1 to 10D . First, referring toFIG. 1 , an entire structure of theimage forming apparatus 100 according to the first embodiment will be described.FIG. 1 is a sectional view schematically illustrating the entire structure of theimage forming apparatus 100 according to the first embodiment of the present invention. - As illustrated in
FIG. 1 , theimage forming apparatus 100 according to the first embodiment includes: asheet feeding portion 8 feeding a sheet S; animage forming portion 14 forming a toner image; a fixingportion 10 fixing a transferred unfixed toner image; and asheet conveying portion 9 as a sheet conveying apparatus. Further, theimage forming apparatus 100 includes asheet discharging portion 13 discharging the sheet S with the toner image fixed thereon. - The
sheet feeding portion 8 includes: apaper feed cassette 80 storing sheets S; afeed roller 81 feeding the sheets S stored in thepaper feed cassette 80 to thesheet conveying portion 9; and a separation portion (not illustrated) separating the sheets S one by one. Thesheet feeding portion 8 uses the separation portion to separate the sheets S stored in thepaper feed cassette 80 one by one which is fed to thesheet conveying portion 9 by thefeed roller 81. - The
image forming portion 14 forms a toner image based on predetermined image information and transfers the toner image to the sheet S to be conveyed on thesheet conveying portion 9. Theimage forming portion 14 includes:photosensitive drums portions exposure portions transfer rollers cleaning portions image forming portion 14 includes atransfer belt 9 a. - Each of the
photosensitive drums photosensitive drums FIG. 1 . The chargingportions photosensitive drums photosensitive drums exposure portions photosensitive drums - The developing portions 4 a, 4 b, 4 c and 4 d include toner containing portions 4 a 1, 4 b 1, 4 c 1 and 4 d 1; and development roller portions 4 a 2, 4
b 2, 4 c 2 and 4d 2 respectively. The toner containing portions 4 a 1, 4 b 1, 4 c 1 and 4 d 1 respectively contain black toner, cyan toner, magenta toner and yellow toner. The development roller portions 4 a 2, 4b 2, 4 c 2 and 4d 2 are adjacently arranged on the respective surfaces of the photosensitive members. Each development roller portion applies a development bias voltage to cause a color toner to adhere to respective electrostatic latent images on thephotosensitive drums - The
transfer rollers transfer belt 9 a so as to abut against thetransfer belt 9 a facing thephotosensitive drums transfer rollers transfer rollers transfer belt 9 a. This electric field causes the respective negative color toner images on thephotosensitive drums photosensitive drums cleaning portions photosensitive drums - According to the present embodiment, the
photosensitive drums portions cleaning portions process cartridge portions - The fixing
portion 10 heats the sheet S with an unfixed toner image transferred thereto to fix the unfixed toner image. Thesheet discharging portion 13 includes a dischargingroller pair discharge portion 13 a onto which the sheet S with the image formed thereon is discharged. - The
sheet conveying portion 9 conveys the sheet S with the toner image formed by theimage forming portion 14. Thesheet conveying portion 9 includes asheet conveying path 15 a, aduplex conveying path 15 b, an obliquefeed roller pair 16, aU-turn roller pair 17, apaper feed frame 20, aguide frame 28, a conveyingroller pair sheet detection portion 22. - The
sheet conveying path 15 a is a conveying path for conveying the sheet S fed from thesheet feeding portion 8 and the sheet S conveyed from theduplex conveying path 15 b, and the toner image formed by theimage forming portion 14 is transferred in a predetermined position therein. Theduplex conveying path 15 b is a conveying path for re-conveying the sheet S inverted by the dischargingroller pair sheet conveying path 15 a for duplex printing. The obliquefeed roller pair 16 is arranged along theduplex conveying path 15 b to convey the inverted sheet S. TheU-turn roller pair 17 is arranged in theduplex conveying path 15 b to re-convey the sheet S conveyed through theduplex conveying path 15 b to thesheet conveying path 15 a. - The
paper feed frame 20 and theguide frame 28 are arranged near an upstream side of theimage forming portion 14 along thesheet conveying path 15 a. The conveying roller pairs 18, 19 are arranged on thesheet conveying path 15 a to convey the sheet S passing through thepaper feed frame 20 and theguide frame 28 to theimage forming portion 14. The conveying roller pairs 18, 19 includes a plurality of conveyingrollers 19 and a plurality of conveyingrotary members 18 facing the plurality of conveyingrollers 19. The conveyingrollers 19 are fixed to arotating shaft 19 a rotatably supported parallel to a rotating shaft direction of thephotosensitive drums shaft 19 a. The conveyingrotary members 18 are rotatably supported to thepaper feed frame 20. The conveyingrotary members 18 are biased to the conveyingrollers 19 by a conveyingrotary member spring 21 attached to thepaper feed frame 20. This biasing force allows the conveyingrotary members 18 to rotate following the conveyingrollers 19 to convey the sheet S. - The
sheet detection portion 22 is arranged on a downstream side in the sheet conveying direction than the conveyingroller pair sheet conveying path 15 a. Thesheet detection portion 22 detects a leading end position of the sheet S conveyed to theimage forming portion 14 by the conveyingroller pair - The sheet S is fed from the
sheet feeding portion 8 to thesheet conveying path 15 a and then conveyed by the conveyingroller pair sheet detection portion 22. Thesheet detection portion 22 detects a leading end position of the sheet S. When the leading end position is detected by thesheet detection portion 22, theimage forming portion 14 starts to form a toner image. When the sheet S passes through thetransfer rollers photosensitive drums portion 10 fixes unfixed toner images to the sheet S, and the sheet S is discharged by the dischargingroller pair discharge portion 13 a. - When performing the duplex printing, the fixing
portion 10 fixes the unfixed toner images to the sheet S, and then the dischargingroller pair roller pair discharge portion 13 a. Thus, the sheet S is conveyed to theduplex conveying path 15 b. The sheet S conveyed along theduplex conveying path 15 b passes through thesheet detection portion 22 by the obliquefeed roller pair 16 and theU-turn roller pair 17, and the sheet S is conveyed again to theimage forming portion 14 to perform duplex printing. - Now, referring to
FIGS. 2A to 3 , thesheet detection portion 22 detecting the leading end position of the sheet S will be specifically described.FIG. 2A is a perspective view illustrating thesheet detection portion 22 supported by the paper feed frame according to the first embodiment.FIG. 2B is a perspective view illustrating thesheet detection portion 22 viewed from an opposite side thereof illustrated inFIG. 2A .FIG. 3 is a perspective view illustrating asensor flag 23 of thesheet detection portion 22 according to the first embodiment. - As illustrated in
FIGS. 2A and 2B , thesheet detection portion 22 includes: asensor flag 23; anoptical sensor 24 as a sensor portion; ashutter driving portion 25; ashutter spring 27 as a biasing portion; and a rotation assistroller 30 as a rotation portion generating a driving force. According to the present embodiment, anassist cam 23 c and the rotation assistroller 30 constitute a rotation transmission portion. - The
sensor flag 23 is supported by thepaper feed frame 20 so as to be positioned on a downstream side of the conveyingroller pair image forming portion 14. As illustrated inFIG. 3 , thesensor flag 23 includes: ashutter flag 23 a as a rotation detection portion; alight shielding portion 23 b as a rotation detection portion; theassist cam 23 c as a transmission portion; and aflag rotating shaft 23 d rotatably supported by thepaper feed frame 20. - The
flag rotating shaft 23 d is arranged parallel to the rotating shaft of thephotosensitive drums paper feed frame 20, and located on a downstream side of the conveyingroller pair shutter flag 23 a is fixed to theflag rotating shaft 23 d, and rotates integrally with theflag rotating shaft 23 d around theflag rotating shaft 23 d. Further, theshutter flag 23 a has an abuttingportion 23 e which is located on a downstream side of the conveyingroller pair roller pair roller pair 18, 19 (seeFIGS. 2A and 2B ). The abuttingportion 23 e has anabutment surface 23 f abutting against the leading end of the sheet S to be conveyed from the conveyingroller pair abutment surface 23 f of the abuttingportion 23 e is pushed by the leading end of the sheet S, theshutter flag 23 a rotates around theflag rotating shaft 23 d. - The
light shielding portion 23 b shields an optical path L of the optical sensor. Thelight shielding portion 23 b is fixed to theflag rotating shaft 23 d and rotates integrally with theflag rotating shaft 23 d around theflag rotating shaft 23 d. Further, thelight shielding portion 23 b has aslit portion 23 g allowing passage of light from theoptical sensor 24. Theslit portion 23 g is formed so as to allow passage of light from theoptical sensor 24 when theabutment surface 23 f of the abuttingportion 23 e provided in theshutter flag 23 a is positioned at a waiting position (hereinafter also referred to as a “home position”) of abutting against the sheet S (seeFIG. 4D described later). More specifically, when theshutter flag 23 a rotates by being pushed by the leading end of the sheet S, thelight shielding portion 23 b shields the optical path L of theoptical sensor 24. Hereinafter, the position of the sensor flag 23 (seeFIGS. 4A to 4D ) in which theabutment surface 23 f of the abuttingportion 23 e is positioned at the home position so as to cause the leading end of the sheet S to abut against theabutment surface 23 f is referred to as a standby position of thesensor flag 23. The urging force of theshutter spring 27 acts to maintain that thesensor flag 23 is located in the home position. - The
assist cam 23 c is fixed to theflag rotating shaft 23 d and rotates integrally with theflag rotating shaft 23 d around theflag rotating shaft 23 d. Further, theassist cam 23 c has an engagingportion 23 h engageable with the rotation assistroller 30. The engagingportion 23 h engages with the rotation assistroller 30 after theabutment surface 23 f of theshutter flag 23 a is pushed by the sheet S to rotate up to a predetermined rotational position until adrive projection portion 25 b (described later) of theshutter driving portion 25 rotates over the top dead center. The predetermined rotational position refers to a rotational position at which rotation of theshutter flag 23 a causes rotation of thelight shielding portion 23 b, causing the optical path L of theoptical sensor 24 to be shielded by thelight shielding portion 23 b. - The
optical sensor 24 is arranged in a rotation path of thelight shielding portion 23 b. Theoptical sensor 24 includes a light emitting portion emitting light; and a light receiving portion receiving the light emitted from the light emitting portion. The light emitted from the light emitting portion is received by the light receiving portion to form the optical path L. When the light shielding portion shields the light emitted from the light emitting portion, a signal (light signal) output from the light emitting portion is shielded, and the received signal changes. Theshutter driving portion 25 is connected to an end portion of theflag rotating shaft 23 d. Theshutter driving portion 25 includes a disc-shapeddrive base portion 25 a, and thedrive projection portion 25 b to which one end of theshutter spring 27 is attached. Thedrive base portion 25 a is connected to theflag rotating shaft 23 d such that the central axis matches theflag rotating shaft 23 d. Thedrive base portion 25 a rotates with theflag rotating shaft 23 d. Thedrive projection portion 25 b is attached to an upper surface of thedrive base portion 25 a such that thedrive projection portion 25 b rotates along an outer periphery of thedrive base portion 25 a around theflag rotating shaft 23 d when rotation of theflag rotating shaft 23 d rotates thedrive base portion 25 a. Thedrive projection portion 25 b is attached to thedrive base portion 25 a such that theabutment surface 23 f of theshutter flag 23 a is positioned at the home position at the bottom dead center. - One end of the
shutter spring 27 is attached to thedrive projection portion 25 b and the other end thereof is attached to thepaper feed frame 20. Theshutter spring 27 biases thedrive projection portion 25 b such that theabutment surface 23 f of theshutter flag 23 a is positioned at the home position. Specifically, theshutter spring 27 biases thedrive projection portion 25 b such that the abuttingportion 23 e of theshutter flag 23 a is positioned at the home position at the bottom dead center of thedrive projection portion 25 b, that is, thesensor flag 23 is positioned at the standby position. - The rotation assist
roller 30 is arranged parallel to the rotating shaft direction of thephotosensitive drums paper feed frame 20. Further, the rotation assistroller 30 is rotated by an not-illustrated drive portion (motor) in a direction indicated by an arrow r as illustrated inFIG. 2A . - Referring to
FIGS. 4A to 10D , the operation of thesheet detection portion 22 will be described.FIG. 4A illustrates thesheet detection portion 22 according to the first embodiment.FIG. 4B illustrates theassist cam 23 c and the rotation assistroller 30 in a state illustrated inFIG. 4A .FIG. 4C illustrates the abuttingportion 23 e of theshutter flag 23 a in a state illustrated inFIG. 4A .FIG. 4D illustrates thelight shielding portion 23 b in a state illustrated inFIG. 4A .FIG. 5A illustrates a state in which the sheet S abuts against theshutter flag 23 a.FIG. 5B illustrates theassist cam 23 c and the rotation assistroller 30 in a state illustrated inFIG. 5A .FIG. 5C illustrates the abuttingportion 23 e of theshutter flag 23 a in a state illustrated inFIG. 5A .FIG. 5D illustrates thelight shielding portion 23 b in a state illustrated inFIG. 5A .FIG. 6A illustrates a state in which thesensor flag 23 rotates to shield the optical path L of theoptical sensor 24.FIG. 6B illustrates theassist cam 23 c and the rotation assistroller 30 in a state illustrated inFIG. 6A .FIG. 6C illustrates theshutter flag 23 a in a state illustrated inFIG. 6A .FIG. 6D illustrates thelight shielding portion 23 b in a state illustrated inFIG. 6A . -
FIG. 7A illustrates a state in which theassist cam 23 c engages with the rotation assistroller 30.FIG. 7B illustrates theassist cam 23 c and the rotation assistroller 30 in a state illustrated inFIG. 7A .FIG. 7C illustrates theshutter flag 23 a in a state illustrated inFIG. 7A .FIG. 7D illustrates thelight shielding portion 23 b in a state illustrated inFIG. 7A .FIG. 8A illustrates a state in which theassist cam 23 c is disengaged from the rotation assistroller 30.FIG. 8B illustrates theassist cam 23 c and the rotation assistroller 30 in a state illustrated inFIG. 8A .FIG. 8C illustrates theshutter flag 23 a in a state illustrated inFIG. 8A .FIG. 8D illustrates thelight shielding portion 23 b in a state illustrated inFIG. 8A . -
FIG. 9A illustrates a state in which the abuttingportion 23 e of theshutter flag 23 a abuts against the sheet S and enters a wait state.FIG. 9B illustrates theassist cam 23 c and the rotation assistroller 30 in a state illustrated inFIG. 9A .FIG. 9C illustrates theshutter flag 23 a in a state illustrated inFIG. 9A .FIG. 9D illustrates thelight shielding portion 23 b in a state illustrated inFIG. 9A .FIG. 10A illustrates a state in which the trailing end of the sheet S passes through theshutter flag 23 a.FIG. 10B illustrates theassist cam 23 c and the rotation assistroller 30 in a state illustrated inFIG. 10A .FIG. 10C illustrates theshutter flag 23 a in a state illustrated inFIG. 10A .FIG. 10D illustrates thelight shielding portion 23 b in a state illustrated inFIG. 10A . - As illustrated in
FIGS. 4A and 4C , in the state in which the leading end of the sheet S does not abut against theabutment surface 23 f of theshutter flag 23 a, the biasing force of theshutter spring 27 causes the abuttingportion 23 e of theshutter flag 23 a to be held in a wait state at the home position. As illustrated in FIG. 4B, at the home position, theassist cam 23 c is spaced apart from the rotation assistroller 30, and the rotational driving force of the rotation assistroller 30 is not transmitted to the engagingportion 23 h of theassist cam 23 c. Further, as illustrated inFIG. 4D , the optical path L of theoptical sensor 24 is allowed to pass through theslit portion 23 g of thelight shielding portion 23 b. - As illustrated in
FIG. 5A , the conveying force of the conveyingroller pair abutment surface 23 f of theshutter flag 23 a is pushed by the leading end of the sheet S, the sheet S rotates theshutter flag 23 a in a direction indicated by an arrow z as illustrated inFIG. 5A . At this time, the sheet S is conveyed against the holding force of theshutter driving portion 25 biased by theshutter spring 27. As illustrated inFIG. 5D , the leading end of the sheet S is guided by a paper feed guide including thepaper feed frame 20 and theguide frame 28 and arranged downstream in the sheet conveying direction of the conveyingroller pair FIG. 5C , the paper feed guide can prevent the leading end of the sheet S from moving away from theabutment surface 23 f and allows the leading end of the sheet S to surely push and rotate theshutter flag 23 a. As illustrated inFIG. 5B , also in this state, theassist cam 23 c is spaced apart from the rotation assistroller 30, and the rotational driving force of the rotation assistroller 30 is not transmitted to the engagingportion 23 h of theassist cam 23 c. - As illustrated in
FIGS. 6A and 6C , theabutment surface 23 f is pushed by the leading end of the sheet S and theshutter flag 23 a rotates against the biasing force of theshutter spring 27. Then, as illustrated inFIG. 6D , the optical path L of theoptical sensor 24 is shielded by thelight shielding portion 23 b. When the optical path L of theoptical sensor 24 is shielded, thesheet detection portion 22 detects that theshutter flag 23 a rotates up to a predetermined rotational position and the leading end of the sheet S is conveyed up to a desired position. Then, thesheet detection portion 22 sends a predetermined signal to theimage forming portion 14. When this signal is received, theimage forming portion 14 starts to form a toner image. As illustrated inFIG. 6B , also in this state, theassist cam 23 c is spaced apart from the rotation assistroller 30, and the rotational driving force of the rotation assistroller 30 is not transmitted to the engagingportion 23 h of theassist cam 23 c. - As illustrated in
FIG. 7A , when the shutter flag further rotates, the engagingportion 23 h of theassist cam 23 c engages with the rotation assistroller 30 rotating in a direction indicated by an arrow r. As illustrated inFIG. 7B , when the engagingportion 23 h of theassist cam 23 c engages with the rotation assistroller 30, the rotational driving force of the rotation assistroller 30 is transmitted to the engagingportion 23 h and theassist cam 23 c rotates in a direction indicated by an arrow z, namely, in the same direction as the rotational direction of being pushed and rotated by the leading end of the sheet S. At a time when the engagingportion 23 h engages with the rotation assistroller 30, the force for rotating thesensor flag 23 is switched from the conveying force of the sheet S to the rotational driving force of the rotation assistroller 30, the state of which continues up to the state in which thedrive projection portion 25 b of theshutter driving portion 25 exceeds the top dead center. The rotation of theassist cam 23 c rotates thesensor flag 23 in the same direction (as the direction indicated by an arrow z), causing the abuttingportion 23 e (abutment surface 23 f) of theshutter flag 23 a to retract from the sheet S. As illustrated inFIGS. 7C and 7D , in this state, also the optical path L of theoptical sensor 24 is shielded by thelight shielding portion 23 b. - As illustrated in
FIG. 8A , thedrive projection portion 25 b of theshutter driving portion 25 reaches the top dead center. At substantially the same time, as illustrated inFIG. 8B , the engagingportion 23 h of theassist cam 23 c becomes spaced apart from the rotation assistroller 30. When the engagingportion 23 h becomes spaced apart from the rotation assistroller 30, the subsequent rotation of thesensor flag 23 is performed by the biasing force of theshutter spring 27. As illustrated inFIGS. 8C and 8D , also in this state, the optical path L of theoptical sensor 24 is shielded by thelight shielding portion 23 b. - The
sensor flag 23 is rotated by the biasing force of theshutter spring 27 in a direction indicated by an arrow z as illustrated inFIG. 8A . Then, as illustrated inFIGS. 9A and 9B , the abuttingportion 23 e of theshutter flag 23 a abuts against the surface of the sheet S conveyed by the conveyingroller pair shutter spring 27 biases thesensor flag 23 to return thesensor flag 23 to the standby position, but thesensor flag 23 cannot return to the standby position because the sheet S being conveyed is positioned on the rotation path. As illustrated inFIG. 9 , the state (position) in which rotation is limited by abutting against the surface of the sheet S during passage is referred to as a sheet passing position of thesensor flag 23. As illustrated inFIG. 9D , also in this state, the optical path L of theoptical sensor 24 is shielded by thelight shielding portion 23 b. - Along with a further conveyance of the sheet S and a passage of the trailing end of the sheet S through the
shutter flag 23 a (passing a position of contacting the abutting portion), as illustrated inFIGS. 10A to 10C , theshutter flag 23 a rotates in a direction indicated by an arrow z by the biasing force of theshutter spring 27. When theshutter flag 23 a rotates in a direction indicated by an arrow z, as illustrated inFIG. 10D , thelight shielding portion 23 b is released from shielding of the optical path L of theoptical sensor 24. Then, theoptical sensor 24 generates a transmission signal. Thus, the trailing end of the sheet S can be detected. - When the trailing end of the sheet S moves further away from the
shutter flag 23 a as illustrated inFIGS. 10A to 10D , thesensor flag 23 is rotated by a rotational force generated by theshutter spring 27 and theshutter driving portion 25. Then, thesensor flag 23 enters a wait state at the standby position for theabutment surface 23 f of theshutter flag 23 a to abut against the subsequent sheet S as illustrated inFIG. 4 . - The
image forming apparatus 100 according to the first embodiment having the above configuration can exert the following effects. Thesheet detection portion 22 according to the first embodiment is configured such that thesensor flag 23 rotates in one direction and returns to the standby position by receiving a rotational driving force from the rotation assistroller 30, theassist cam 23 c, and theshutter spring 27 constituting the rotation transmission portion. Specifically, thesensor flag 23 rotates to enter a wait state of being in contact with a sheet near the standby position. When the sheet S passes, thesensor flag 23 moves to the standby position. Consequently, the sensor flag can return to the standby position in a shorter time than the sensor flag takes to reciprocate. Thus, an increase in sheet gap distance can be prevented when increasing the conveying speed of the sheet S. More specifically, thesensor flag 23 can return to the standby position in a short sheet gap, which has been conventionally difficult under high sheet conveying speed conditions. As a result, throughput can be improved. - For example, the first embodiment can shorten the sheet gap to about half in comparison with a conventional sensor flag performing a reciprocating movement. Thus, the first embodiment can meet user demands to further improve throughput of the image forming apparatus. The
assist cam 23 c assists rotation to prevent a biasing force from being applied to the leading end of the sheet after skew correction, thus preventing damage such as scratching and folding from occurring in the leading end of the sheet. - According to the first embodiment, the
assist cam 23 c and the rotation assistroller 30 are used to transmit a rotational driving force to thesensor flag 23 and the biasing force of theshutter spring 27 is used to return thesensor flag 23 to the home position. Consequently, the rotational driving force can be transmitted to the sensor flag by a simple configuration. Thus, manufacturing costs can be suppressed or manufacturing at a low price is enabled. - An
image forming apparatus 100A according to a second embodiment of the present invention will be described referring toFIGS. 11 to 14D .FIG. 11 is a perspective view illustrating asheet detection portion 22A supported by apaper feed frame 20 according to the second embodiment.FIG. 12 is a perspective view illustrating asensor flag 23A of thesheet detection portion 22A according to the second embodiment.FIG. 13A illustrates thesheet detection portion 22A according to the second embodiment.FIG. 13B illustrates anassist cam 23 c and a rotation assistroller 30 in a state illustrated inFIG. 13A .FIG. 13C illustrates an abuttingportion 223 e of ashutter flag 223 a in a state illustrated inFIG. 13A .FIG. 13D illustrates alight shielding portion 23 b in a state illustrated inFIG. 13A . -
FIG. 14A illustrates a state in which the abuttingportion 223 e of theshutter flag 223 a abuts against a sheet S and enters a wait state.FIG. 14B illustrates theassist cam 23 c and the rotation assistroller 30 in a state illustrated inFIG. 14A .FIG. 14C illustrates theshutter flag 223 a in a state illustrated inFIG. 14A .FIG. 14D illustrates thelight shielding portion 23 b in a state illustrated inFIG. 14A . - The second embodiment is different from the first embodiment in that the
sheet detection portion 22A of the second embodiment has aflag rotary member 223 k on a tip of anabutting portion 223 e of ashutter flag 223 a. Thus, the description of the second embodiment will focus on the difference from the first embodiment, namely, theflag rotary member 223 k provided on theshutter flag 223 a. In the second embodiment, the same reference numerals or characters are assigned to the same components as those of theimage forming apparatus 100 according to the first embodiment and the description thereof is omitted. In the second embodiment, the same components as those of the first embodiment exert the same effects as those of the first embodiment. - Referring to
FIG. 1 , the entire structure of theimage forming apparatus 100A according to the second embodiment will be described. As illustrated inFIGS. 1 and 11 , theimage forming apparatus 100A according to the second embodiment includes asheet feeding portion 8, animage forming portion 14, a fixingportion 10, asheet conveying portion 9A, and asheet discharging portion 13. - The
sheet conveying portion 9A includes asheet conveying path 15 a, aduplex conveying path 15 b, an obliquefeed roller pair 16, aU-turn roller pair 17, thepaper feed frame 20, aguide frame 28, a conveyingroller pair sheet detection portion 22A. Thesheet detection portion 22A includes thesensor flag 23A, anoptical sensor 24, ashutter driving portion 25, ashutter spring 27, and the rotation assistroller 30. As illustrated inFIG. 12 , thesensor flag 23A includes theshutter flag 223 a, thelight shielding portion 23 b, theassist cam 23 c, and aflag rotating shaft 23 d. - The
shutter flag 223 a includes the abuttingportion 223 e, and theflag rotary member 223 k rotatably supported on the tip of the abuttingportion 223 e. Theflag rotary member 223 k is supported by the abuttingportion 223 e so as to rotate while abutting against the surface of the sheet S to be conveyed. - Referring to
FIGS. 13A to 14D , the operation of thesheet detection portion 22A will be described. As illustrated inFIGS. 13A and 13C , in a state in which the leading end of the sheet S does not abut against an abutment surface 223 f of theshutter flag 223 a, the abuttingportion 223 e of theshutter flag 223 a is held in a wait state at the home position by the biasing force of theshutter spring 27. As illustrated inFIG. 13B , at the home position, theassist cam 23 c is spaced apart from the rotation assistroller 30, and the rotational driving force of the rotation assistroller 30 is not transmitted to the engagingportion 23 h of theassist cam 23 c. Further, as illustrated inFIG. 13D , an optical path L of theoptical sensor 24 is allowed to pass through aslit portion 23 g of thelight shielding portion 23 b. - When the
sensor flag 23 rotates in a direction indicated by an arrow z by the biasing force of theshutter spring 27, as illustrated inFIGS. 14A and 14B , theflag rotary member 223 k of theshutter flag 223 a rolls on and contacts the surface of the sheet S conveyed by the conveyingroller pair shutter spring 27 biases thesensor flag 23A to return thesensor flag 23A to the home position, but thesensor flag 23A cannot return to the home position because the sheet S is conveyed. Accordingly, as illustrated inFIG. 14C , in a state in which theshutter flag 223 a is biased by theshutter spring 27, theflag rotary member 223 k rolls on and contacts the surface of the sheet S to enter a wait state. As illustrated inFIG. 14D , also in this state, the optical path L of theoptical sensor 24 is shielded by thelight shielding portion 23 b. - The
image forming apparatus 100A according to the second embodiment having the above configuration can exert not only the effects resulting from the same configuration as that of the first embodiment but also the following effects. Thesheet detection portion 22A according to the second embodiment has theflag rotary member 223 k on the tip of the abuttingportion 223 e of theshutter flag 223 a. Consequently, even in a state in which thesensor flag 23 rotates and contacts the surface of the sheet S to enter a wait state, theflag rotary member 223 k rolls on and contacts the sheet S, thus preventing the abuttingportion 223 e from contacting the sheet S in a scratching manner. Thus, a contact trace of the abuttingportion 223 e is unlikely to remain to the sheet S. For example, a larger effect can be expected in a case in which the conveyingroller pair portion 223 e of theshutter flag 223 a contacts a toner image surface after the toner image is fixed. - Referring to
FIG. 1 and further referring toFIGS. 15 to 22C , animage forming apparatus 100B according to the third embodiment of the present invention will be described.FIG. 15 is a perspective view illustrating asheet detection portion 22B supported by apaper feed frame 20 according to the third embodiment.FIG. 16 is a perspective view illustrating asensor flag 23B of thesheet detection portion 22B according to the third embodiment.FIG. 17A illustrates thesheet detection portion 22B according to the third embodiment.FIG. 17B illustrates asensor cam 323 i, ashutter spring 327, acam follower 336, and apressing member 335 in a state illustrated inFIG. 17A .FIG. 17C illustrates an abuttingportion 323 a and a light shielding portion 323 b of ashutter flag 323 in a state illustrated inFIG. 17A .FIG. 18A illustrates a state in which thesensor flag 23B rotates to shield an optical path of an optical sensor.FIG. 18B illustrates thesensor cam 323 i, theshutter spring 327, thecam follower 336, and the pressing member in a state illustrated inFIG. 18A .FIG. 18C illustrates the abuttingportion 323 a of theshutter flag 323 and the light shielding portion 323 b in a state illustrated inFIG. 18A . -
FIG. 19A illustrates a state in which thesensor cam 323 i engages with a rotation assistroller 30.FIG. 19B illustrates thesensor cam 323 i, theshutter spring 327, thecam follower 336, and thepressing member 335 in a state illustrated inFIG. 19A .FIG. 19C illustrates the abuttingportion 323 a and the light shielding portion 323 b of theshutter flag 323 in a state illustrated inFIG. 19A .FIG. 20A illustrates a state in which thesensor cam 323 i disengages from the rotation assistroller 30.FIG. 20B illustrates the sensor cam, theshutter spring 327, thecam follower 336, and thepressing member 335 in a state illustrated inFIG. 20A .FIG. 20C illustrates the abuttingportion 323 a and the light shielding portion 323 b of theshutter flag 323 in a state illustrated inFIG. 20A . -
FIG. 21A illustrates a state in which the abuttingportion 323 a of theshutter flag 323 abuts against the sheet and enters a wait state.FIG. 21B illustrates thesensor cam 323 i, theshutter spring 327, thecam follower 336, and thepressing member 335 in a state illustrated inFIG. 21A .FIG. 21C illustrates the abuttingportion 323 a and the light shielding portion 323 b of theshutter flag 323 in a state illustrated inFIG. 21A .FIG. 22A illustrates a state in which the trailing end of a sheet S passes through theshutter flag 323.FIG. 22B illustrates thesensor cam 323 i, theshutter spring 327, thecam follower 336, and thepressing member 335 in a state illustrated inFIG. 22A .FIG. 22C illustrates the abuttingportion 323 a and the light shielding portion 323 b of theshutter flag 323 in a state illustrated inFIG. 22A . - The third embodiment is different from the first embodiment in that the
image forming apparatus 100B according to the third embodiment provides thesensor cam 323 i, theshutter spring 327, the pressingmember 335, and thecam follower 336 to exert a biasing force to bias the shutter flag 223. Further, the third embodiment is different from the first embodiment in the shape of thesensor flag 23B. Thus, the description of the third embodiment will focus on the differences from the first embodiment. In the third embodiment, the same reference numerals or characters are assigned to the same components as those of theimage forming apparatus 100 according to the first embodiment and the description thereof is omitted. That is, in the third embodiment, the same components as those of the first embodiment exert the same effects as those of the first embodiment. - Referring to
FIG. 1 , the entire structure of theimage forming apparatus 100B according to the third embodiment will be described. As illustrated inFIGS. 1 and 15 , theimage forming apparatus 100B according to the third embodiment includes asheet feeding portion 8, animage forming portion 14, a fixingportion 10, asheet conveying portion 9B, and asheet discharging portion 13. - The
sheet conveying portion 9B includes asheet conveying path 15 a, aduplex conveying path 15 b, an obliquefeed roller pair 16, aU-turn roller pair 17, thepaper feed frame 20, aguide frame 28, a conveyingroller pair sheet detection portion 22B. Thesheet detection portion 22B includes thesensor flag 23B, anoptical sensor 24, theshutter spring 327, the pressingmember 335, thecam follower 336, and the rotation assistroller 30. As illustrated inFIG. 16 , thesensor flag 23B includes theshutter flag 323, the light shielding portion 323 b, anassist cam 323 c, thesensor cam 323 i, and aflag rotating shaft 23 d. - The
shutter flag 323 includes the abuttingportion 323 a and the light shielding portion 323 b. The abuttingportion 323 a includes an abuttingportion 323 a 1, an abuttingportion 323 a 2, and anabutting portion 323 a 3. The light shielding portion 323 b includes a light shielding portion 323 b 1, a light shielding portion 323b 2, and a light shielding portion 323 b 3. Theassist cam 323 c includes an engagingportion 323 c 1, an engagingportion 323 c 2, and an engagingportion 323 c 3 to engage with the rotation assistroller 30. Thesensor cam 323 i is fixed to theflag rotating shaft 23 d and rotates integrally with theflag rotating shaft 23 d. Thesensor cam 323 i uses theshutter spring 327, thecam follower 336, and thepressing member 335 to exert a biasing force to bias thesensor flag 23B. - Referring to
FIGS. 17A to 22C , the operation of thesheet detection portion 22B will be described. As illustrated inFIG. 17A , in a state in which the leading end of the sheet S does not abut against the abuttingportion 323 a of theshutter flag 323, the abuttingportion 323 a of theshutter flag 323 is held in a wait state at the home position by the biasing force of theshutter spring 27. At the home position, theassist cam 323 c is spaced apart from the rotation assistroller 30, and the rotational driving force of the rotation assistroller 30 is not transmitted to any of the engagingportion 323 c 1, the engagingportion 323 c 2, and the engagingportion 323 c 3 of theassist cam 323 c. As illustrated inFIG. 17C , an optical path L of theoptical sensor 24 enters a state of not being shielded by any of the light shielding portion 323 b 1, the light shielding portion 323b 2, and the light shielding portion 323 b 3 of theshutter flag 323. - As illustrated in
FIGS. 18A and 18C , when the sheet S pushes the abuttingportion 323 a 1 of theshutter flag 323 in a direction indicated by an arrow z and theshutter flag 323 rotates against the biasing force of theshutter spring 327, the optical path L is shielded by the light shielding portion 323b 2. When the optical path L of theoptical sensor 24 is shielded, thesheet detection portion 22B detects that theshutter flag 323 rotates up to a predetermined rotational position and the leading end of the sheet S is conveyed up to a desired position. Then, thesheet detection portion 22B sends a predetermined signal to theimage forming portion 14. When this signal is received, theimage forming portion 14 starts to form a toner image. As illustrated inFIG. 18A , also in this state, theassist cam 323 c is spaced apart from the rotation assistroller 30, and the rotational driving force of the rotation assistroller 30 is not transmitted to the engagingportion 323 c 1 of theassist cam 323 c. - As illustrated in
FIG. 19A , theshutter flag 323 is further rotated by the leading end of the sheet S, the engagingportion 323 c 1 of theassist cam 323 c engages with the rotation assistroller 30 rotating in a direction indicated by an arrow r. When the engagingportion 323 c 1 of theassist cam 323 c engages with the rotation assistroller 30, the rotational driving force of the rotation assistroller 30 is transmitted to the engagingportion 323 c 1 and theassist cam 323 c rotates in a direction indicated by an arrow z. At a time when the engagingportion 323 c 1 engages with the rotation assistroller 30, the force for rotating thesensor flag 23B is switched from the conveying force of the sheet S to the rotational driving force of the rotation assistroller 30. The rotation continues up to the state in which thesensor cam 323 i exceeds the top dead center. The rotation of theassist cam 323 c rotates theshutter flag 323 in the same direction (as the direction indicated by an arrow z), causing the abuttingportion 323 a 1 of theshutter flag 323 to retract from the sheet S. As illustrated inFIG. 19C , also in this state, the optical path L of theoptical sensor 24 is shielded by the light shielding portion 323b 2. As illustrated inFIG. 19B , thesensor cam 323 i also rotates in a direction indicated by an arrow z, and thus thesensor cam 323 i assists in pushing down thecam follower 336, the pressingmember 335, and theshutter spring 327. - As illustrated in
FIGS. 20A and 20B , thesensor cam 323 i reaches the top dead center. At substantially the same time, as illustrated inFIG. 20A , the engagingportion 323 c 1 of theassist cam 323 c becomes spaced apart from the rotation assistroller 30. When the engagingportion 323 c 1 becomes spaced apart from the rotation assistroller 30, the biasing force of thecam follower 336, the pressingmember 335, and theshutter spring 327 pushes up thesensor cam 323 i to rotate theshutter flag 323. As illustrated inFIG. 20C , also in this state, the optical path L of theoptical sensor 24 is shielded by the light shielding portion 323b 2. - When the biasing force of the
cam follower 336, the pressingmember 335, and theshutter spring 327 pushes up thesensor cam 323 i, the abuttingportion 323 a 2 of theshutter flag 323 enters a state of contacting the surface of the sheet S as illustrated inFIGS. 21A to 21C . At this time, the biasing force of theshutter spring 327 and the like biases the abuttingportion 323 a 2 of theshutter flag 323 to return to the home position, but the abuttingportion 323 a 2 of theshutter flag 323 cannot return to the home position because the sheet S is conveyed. Accordingly, as illustrated inFIG. 21C , the abuttingportion 323 a 2 of theshutter flag 323 enters a state of being biased by theshutter spring 327 and the like to abut against the surface of the sheet S in a wait state. As illustrated inFIG. 21C , also in this state, the optical path L of theoptical sensor 24 is also shielded by the light shielding portion 323b 2. - When the sheet S is further conveyed and the trailing end of the sheet S passes through the
shutter flag 323, theshutter flag 323 rotates in a direction indicated by an arrow z as illustrated inFIGS. 22A to 22C . When theshutter flag 323 rotates in a direction indicated by an arrow z, the light shielding portion 323b 2 is released from shielding of the optical path L of theoptical sensor 24 as illustrated inFIG. 22C . Then, theoptical sensor 24 generates a transmission signal. Thus, the trailing end of the sheet S can be detected. - When the trailing end of the sheet S moves away from the
shutter flag 323 as illustrated inFIGS. 22A to 22C , thesensor flag 23B is rotated by a rotational force generated by theshutter spring 327, thesensor cam 323 i, and the like. Then, thesensor flag 23B enters a wait state at the home position for the abuttingportion 323 a 2 of theshutter flag 323 to abut against a leading end of the subsequent sheet S as illustrated inFIG. 17A . - The
image forming apparatus 100B according to the third embodiment having the above configuration can exert not only the effects resulting from the same configuration as that of the first embodiment but also the following effects. Thesheet detection portion 22B according to the third embodiment includes theshutter flag 323 having the abuttingportions 323 a 1, 323 a 2 and 323 a 3, and the light shielding portions 323 b 1, 323 b 2 and 323 b 3; theassist cam 323 c having the engagingportions 323 c 1, 323 c 2 and 323 c 3; and thesensor cam 323 i. Accordingly, thesheet detection portion 22B can detect the leading end of the sheet S without a whole turn of thesensor flag 23B. Thus, it can take less time to position the abuttingportion 323 a at the home position, and an increase in sheet gap distance can be prevented when increasing the conveying speed of the sheet S. As a result, throughput can be improved. - According to the
sheet detection portion 22B of the third embodiment, even the configuration of biasing theshutter flag 323 by using theshutter spring 327 and theassist cam 323 c can assist theshutter flag 323 in giving thesensor cam 323 i a force for rolling over the top dead center. Use of theassist cam 323 c to assist the rotation can eliminate the need for the force for pushing theshutter flag 323 to depend only on stiffness of the sheet S, thus preventing damage such as scratching and folding from occurring in the leading end of the sheet S. - Referring to
FIG. 1 and further referring toFIGS. 23A to 26D , animage forming apparatus 100C according to a fourth embodiment of the present invention will be described.FIG. 23A is a perspective view illustrating asheet detection portion 22C supported by a paper feed frame according to the fourth embodiment.FIG. 23B is a perspective view illustrating thesheet detection portion 22C viewed from an opposite side thereof illustrated inFIG. 23A .FIG. 24A illustrates thesheet detection portion 22C according to the fourth embodiment.FIG. 24B illustrates an assist gear and a rotation assist gear in a state illustrated inFIG. 24A .FIG. 24C illustrates an abuttingportion 23 e of a shutter flag in a state illustrated inFIG. 24A .FIG. 24D illustrates a light shielding portion in a state illustrated inFIG. 24A . -
FIG. 25A illustrates a state in which the assist gear engages with the rotation assist gear.FIG. 25B illustrates the assist gear and the rotation assist gear in a state illustrated inFIG. 25A .FIG. 25C illustrates the shutter flag in a state illustrated inFIG. 25A .FIG. 25D illustrates the light shielding portion in a state illustrated inFIG. 25A .FIG. 26A illustrates a state in which the abuttingportion 23 e of the shutter flag abuts against a sheet and enters a wait state.FIG. 26B illustrates the assist gear and the rotation assist gear in a state illustrated inFIG. 26A .FIG. 26C illustrates the shutter flag in a state illustrated inFIG. 26A .FIG. 26D illustrates the light shielding portion in a state illustrated inFIG. 26A . - The fourth embodiment is different from the first embodiment in that the
image forming apparatus 100C of the fourth embodiment uses anassist gear 423 c and arotation assist gear 430. Thus, the description of the fourth embodiment will focus on the difference from the first embodiment, namely, theassist gear 423 c and the rotation assistgear 430. In the fourth embodiment, the same reference numerals or characters are assigned to the same components as those of theimage forming apparatus 100 according to the first embodiment and the description thereof is omitted. In the fourth embodiment, the same components as those of the first embodiment exert the same effects as those of the first embodiment. - Referring to
FIG. 1 , the entire structure of theimage forming apparatus 100C according to the fourth embodiment will be described. As illustrated inFIG. 1 andFIGS. 23A to 26D , theimage forming apparatus 100C according to the fourth embodiment includes asheet feeding portion 8, animage forming portion 14, a fixingportion 10, asheet conveying portion 9C, and asheet discharging portion 13. - The
sheet conveying portion 9C includes asheet conveying path 15 a, aduplex conveying path 15 b, an obliquefeed roller pair 16, aU-turn roller pair 17, thepaper feed frame 20, aguide frame 28, a conveyingroller pair sheet detection portion 22C. Thesheet detection portion 22C includes asensor flag 23C, anoptical sensor 24, ashutter driving portion 25, ashutter spring 27, and the rotation assistgear 430 as a rotation portion. Thesensor flag 23C includes ashutter flag 23 a, alight shielding portion 23 b, theassist gear 423 c, and aflag rotating shaft 23 d. - The
rotation assist gear 430 is formed into a gear shape whose outer peripheral surface has a plurality of teeth. Theassist gear 423 c is arranged in a predetermined range of the outer peripheral surface thereof and includes an interruptedtoothed portion 423 h as an interrupted toothed gear meshing with the rotation assistgear 430. After anabutment surface 23 f of theshutter flag 23 a is pushed by a sheet S to rotate up to a predetermined rotational position, the interruptedtoothed portion 423 h engages with the rotation assistgear 430 until adrive projection portion 25 b of theshutter driving portion 25 rotates and exceeds the top dead center. - Referring to
FIGS. 24A to 26D , the operation of thesheet detection portion 22C will be described. As illustrated inFIGS. 24A and 24C , in a state in which the leading end of the sheet S does not abut against theabutment surface 23 f of theshutter flag 23 a, the abuttingportion 23 e of theshutter flag 23 a is held in a wait state at the home position by the biasing force of theshutter spring 27. As illustrated inFIG. 24B , at the home position, the interruptedtoothed portion 423 h of theassist gear 423 c is spaced apart from the rotation assistgear 430, and the rotational driving force of the rotation assistgear 430 is not transmitted to the interruptedtoothed portion 423 h of theassist gear 423 c. Further, as illustrated inFIG. 24D , an optical path L of theoptical sensor 24 is allowed to pass through aslit portion 23 g of thelight shielding portion 23 b. - As illustrated in
FIG. 25A , when theshutter flag 23 a further rotates, the interruptedtoothed portion 423 h of theassist gear 423 c engages with the rotation assistgear 430 rotating in a direction indicated by an arrow r. As illustrated inFIG. 25B , when the interruptedtoothed portion 423 h of theassist gear 423 c engages with the rotation assistgear 430, the rotational driving force of the rotation assistgear 430 is transmitted to the interruptedtoothed portion 423 h and theassist gear 423 c rotates in a direction indicated by an arrow z. At a time when the interruptedtoothed portion 423 h engages with the rotation assistgear 430, the force for rotating thesensor flag 23C is switched from the conveying force of the sheet S to the rotational driving force of the rotation assistgear 430, the state of which continues up to the state in which thedrive projection portion 25 b of theshutter driving portion 25 exceeds the top dead center. As illustrated inFIG. 25C , the rotation of theassist gear 423 c rotates thesensor flag 23C in the same direction (as the direction indicated by an arrow z), causing the abuttingportion 23 e (abutment surface 23 f) of theshutter flag 23 a to retract from the sheet S. As illustrated inFIG. 25D , also in this state, the optical path L of theoptical sensor 24 is shielded by thelight shielding portion 23 b. - At substantially the same time as when the
drive projection portion 25 b of theshutter driving portion 25 reaches the top dead center, the interruptedtoothed portion 423 h of theassist gear 423 c becomes spaced apart from the rotation assistgear 430. When the interruptedtoothed portion 423 h becomes spaced apart from the rotation assistgear 430, the subsequent rotation of thesensor flag 23C is performed by the biasing force of theshutter spring 27. When thesensor flag 23C rotates in a direction indicated by an arrow z by the biasing force of theshutter spring 27, as illustrated inFIGS. 26A and 26B , the abuttingportion 23 e of theshutter flag 23 a abuts against the surface of the sheet S conveyed by the conveyingroller pair shutter spring 27 biases theshutter flag 23 a to return theshutter flag 23 a to the home position, but theshutter flag 23 a cannot return to the home position until the sheet S passes therethrough because the sheet S is conveyed. Accordingly, as illustrated inFIG. 26C , in a state of being biased by theshutter spring 27, theshutter flag 23 a abuts against the surface of the sheet S to enter a wait state. As illustrated inFIG. 26D , also in this state, the optical path L of theoptical sensor 24 is shielded by thelight shielding portion 23 b. - When the sheet S is further conveyed and the trailing end of the sheet S passes through the
shutter flag 23 a, theshutter flag 23 a rotates in a direction indicated by an arrow z. When theshutter flag 23 a rotates in a direction indicated by an arrow z, thelight shielding portion 23 b is released from shielding of the optical path L of theoptical sensor 24. Then, theoptical sensor 24 generates a transmission signal. Thus, the trailing end of the sheet S can be detected. - When the trailing end of the sheet S moves away from the
shutter flag 23 a, thesensor flag 23C is rotated by a rotational force generated by theshutter spring 27 and theshutter driving portion 25. Then, theabutment surface 23 f of theshutter flag 23 a enters a wait state at the home position for detecting the subsequent sheet S as illustrated inFIG. 24A . - The
image forming apparatus 100C according to the fourth embodiment having the above configuration can exert not only the effects resulting from the same configuration as that of the first embodiment but also the following effects. Thesheet detection portion 22C according to the fourth embodiment meshes the rotation assistgear 430 with the interruptedtoothed portion 423 h of theassist gear 423 c to rotate thesensor flag 23C. Accordingly, the fourth embodiment can suppress slippage due to wear of rollers and cams more than the configuration of engaging the rotation assistroller 30 with theassist cam 23 c. Thus, the fourth embodiment can assure more reliable meshing and can increase meshing reliability. - Referring to
FIG. 1 and further referring toFIGS. 27 to 29 , the entire structure of animage forming apparatus 100D according to a fifth embodiment of the present invention will be described.FIG. 27 is a perspective view illustrating asheet detection portion 22D supported by apaper feed frame 20 according to the fifth embodiment.FIG. 28 is a perspective view illustrating asensor flag 23D of thesheet detection portion 22D according to the fifth embodiment.FIG. 29 illustrates thesheet detection portion 22D according to the fifth embodiment. - The
image forming apparatus 100D of the fifth embodiment is different from the first embodiment in that alight shielding portion 23 b and aslit portion 23 g are provided on ashutter flag 123 a having an abuttingportion 23 e. Thus, the description of the fifth embodiment will focus on the difference from the first embodiment, namely, theshutter flag 123 a. In the fifth embodiment, the same reference numerals or characters are assigned to the same components as those of theimage forming apparatus 100 according to the first embodiment and the description thereof is omitted. That is, in the fifth embodiment, the same components as those of the first embodiment exert the same effects as those of the first embodiment. - Referring to
FIG. 1 , the entire structure of theimage forming apparatus 100D according to the fifth embodiment will be described. As illustrated inFIGS. 1 and 27 , theimage forming apparatus 100D according to the fifth embodiment includes asheet feeding portion 8, animage forming portion 14, a fixingportion 10, asheet conveying portion 9D, and asheet discharging portion 13. - The
sheet conveying portion 9D includes asheet conveying path 15 a, aduplex conveying path 15 b, an obliquefeed roller pair 16, aU-turn roller pair 17, thepaper feed frame 20, aguide frame 28, a conveyingroller pair sheet detection portion 22D. Thesheet detection portion 22D includes thesensor flag 23D, anoptical sensor 24, ashutter driving portion 25, ashutter spring 27, and a rotation assistroller 30. As illustrated inFIG. 28 , thesensor flag 23D includes theshutter flag 123 a, anassist cam 23 c, and aflag rotating shaft 23 d. - The
shutter flag 123 a includes the abuttingportion 23 e which can abut against the leading end of a sheet S conveyed by the conveyingroller pair light shielding portion 23 b as a rotation detection portion; and theslit portion 23 g passing light from theoptical sensor 24. - The
image forming apparatus 100D according to the fifth embodiment having the above configuration can exert not only the effects resulting from the same configuration as that of the first embodiment but also the following effects. In thesheet detection portion 22D according to the fifth embodiment, theshutter flag 123 a and thelight shielding portion 23 b are made of the same member. The abuttingportion 23 e, thelight shielding portion 23 b and theslit portion 23 g are formed from the same member. Accordingly, when providing theshutter flag 123 a, costs can be reduced and space can be saved. - Hereinbefore, the embodiments of the present invention have been described, but the present invention is not limited to the aforementioned embodiments. In addition, the effects described in the embodiments of the present invention are merely a listing of exemplary effects deriving from the present invention and thus the effects of the present invention are not limited to the description of the embodiments of the present invention.
- For example, in the first embodiment, the rotation assist
roller 30 is arranged independently, but the present invention is not limited to this. For example, the rotation assistroller 30 may be arranged on therotating shaft 19 a of the conveyingrollers 19 so as to face theassist cam 23 c integrally formed with thesensor flag 23. This arrangement can reduce costs and save space more than the independent arrangement of the rotation assistroller 30. - In addition, the third embodiment describes that the
sheet detection portion 22B detects the sheet S, and the image is formed so as to be matched with the sheet based on the signal from thesheet detection portion 22B, but the present invention is not limited to this. For example, a configuration may be made such that first, the image formation is performed and after the sheet S is detected by thesheet detection portion 22, the sheet is positioned to the image. - In the present embodiment, the biasing force of the
shutter spring 27 is used to return the sensor flag to the home position, but the present invention is not limited to this. For example, a configuration may be made such that the sensor flag returns to the home position by adjusting the weight balance of the sensor flag or using gravitational force. - In the fourth embodiment, the
shutter spring 27 is mounted on thedrive projection portion 25 b of theshutter driving portion 25, but the present invention is not limited to this. For example, theshutter spring 27 may be mounted on theassist gear 423 c. - While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
- This application claims the benefit of Japanese Patent Application No. 2010-230415, filed Oct. 13, 2010, which is hereby incorporated by reference herein in its entirety.
Claims (8)
1. A sheet conveying apparatus comprising:
a conveying portion configured to convey a sheet;
a rotation detection portion rotatably provided and having an abutting portion which abuts against a leading end of the sheet conveyed by the conveying portion at a waiting position, wherein the rotation detection portion is rotated in a predetermined rotational direction by being pushed by the leading end of the conveyed sheet;
a sensor portion detecting the conveyed sheet based on a rotational position of the rotation detection portion;
a rotation transmission portion configured to transmit a rotational driving force to the rotation detection portion to rotate the rotation detection portion in the predetermined rotational direction after the rotation detection portion is rotated by being pushed by the leading end of the conveyed sheet; and
an urging unit configured to apply an urging force to the rotation detection portion, wherein after the rotation detection portion is rotated by the rotational driving force of the rotation transmission portion, the urging unit applies the urging force to the rotation detection portion so that the rotation detection portion comes into contact with a surface of the sheet, thereafter the rotation detection portion is returned to the waiting position along with the passage of the rear end of the sheet through the rotation detection portion.
2. The sheet conveying apparatus according to claim 1 , wherein, the rotation transmission portion includes:
a rotation portion configured to generate the rotational driving force; and
a transmission portion coupled to the rotation detection portion and configured to transmit the rotational driving force to the rotation detection portion by engaging with the rotating unit,
wherein, after the abutting portion is pushed by the leading end of the sheet and the rotation detection portion rotates up to a predetermined rotational position for changing a signal output from the sensor portion, the transmission portion engages with the rotation portion and applies the rotational driving force to the rotation detection portion, and the transmission portion disengages with the rotation portion in a state in which the rotation detection portion contacts with the surface of the passing sheet by the urging force of the urging unit.
3. The sheet conveying apparatus according to claim 2 , wherein the rotation portion has a gear shape whose outer peripheral surface has a tooth, and
the transmission portion has an interrupted toothed gear arranged in a predetermined range on an outer peripheral surface of the transmission portion and meshing with the tooth of the rotation portion.
4. The sheet conveying apparatus according to claim 1 , wherein the sensor portion has a light emitting portion and a light receiving portion,
wherein the rotation detection portion has a light shielding portion shielding light to be received by the light receiving portion, and
wherein the rotation detection portion rotates and the light shielding portion shields light to be received by the light receiving portion, thereby a leading end position of the conveyed sheet is detected.
5. An image forming apparatus comprising:
the sheet conveying apparatus according to claim 1 ; and
an image forming portion forming an image on the sheet fed out from the sheet conveying apparatus.
6. An image forming apparatus according to claim 5 , wherein, the rotation transmission portion includes:
a rotation portion configured to generate the rotational driving force; and
a transmission portion coupled to the rotation detection portion and configured to transmit the rotational driving force to the rotation detection portion by engaging with the rotating unit,
wherein, after the abutting portion is pushed by the leading end of the sheet and the rotation detection portion rotates up to a predetermined rotational position for changing a signal output from the sensor portion, the transmission portion engages with the rotation portion and applies the rotational driving force to the rotation detection portion, and the transmission portion disengages with the rotation portion in a state in which the rotation detection portion contacts with the surface of the passing sheet by the urging force of the urging unit.
7. An image forming apparatus according to claim 6 , wherein the rotation portion has a gear shape whose outer peripheral surface has a tooth, and
the transmission portion has an interrupted toothed gear arranged in a predetermined range on an outer peripheral surface of the transmission portion and meshing with the tooth of the rotation portion.
8. An image forming apparatus according to claim 5 , wherein the sensor portion has a light emitting portion and a light receiving portion,
wherein the rotation detection portion has a light shielding portion shielding light to be received by the light receiving portion, and
wherein the rotation detection portion rotates and the light shielding portion shields light to be received by the light receiving portion, thereby a leading end position of the conveyed sheet is detected.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US13/750,178 US8556259B2 (en) | 2010-10-13 | 2013-01-25 | Sheet conveying apparatus and image forming apparatus |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2010230415A JP5627384B2 (en) | 2010-10-13 | 2010-10-13 | Sheet conveying apparatus and image forming apparatus |
JP2010-230415 | 2010-10-13 |
Related Child Applications (1)
Application Number | Title | Priority Date | Filing Date |
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US13/750,178 Division US8556259B2 (en) | 2010-10-13 | 2013-01-25 | Sheet conveying apparatus and image forming apparatus |
Publications (2)
Publication Number | Publication Date |
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US20120091652A1 true US20120091652A1 (en) | 2012-04-19 |
US8387975B2 US8387975B2 (en) | 2013-03-05 |
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Application Number | Title | Priority Date | Filing Date |
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US13/249,399 Expired - Fee Related US8387975B2 (en) | 2010-10-13 | 2011-09-30 | Sheet conveying apparatus and image forming apparatus |
US13/750,178 Expired - Fee Related US8556259B2 (en) | 2010-10-13 | 2013-01-25 | Sheet conveying apparatus and image forming apparatus |
Family Applications After (1)
Application Number | Title | Priority Date | Filing Date |
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US13/750,178 Expired - Fee Related US8556259B2 (en) | 2010-10-13 | 2013-01-25 | Sheet conveying apparatus and image forming apparatus |
Country Status (3)
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US (2) | US8387975B2 (en) |
JP (1) | JP5627384B2 (en) |
CN (1) | CN102556703B (en) |
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US8439358B2 (en) | 2011-03-16 | 2013-05-14 | Canon Kabushiki Kaisha | Sheet conveying apparatus and image forming apparatus |
US20150115526A1 (en) * | 2013-10-30 | 2015-04-30 | Canon Kabushiki Kaisha | Sheet conveying apparatus and image forming apparatus |
US11108929B2 (en) * | 2019-12-19 | 2021-08-31 | Toshiba Tec Kabushiki Kaisha | Sheet conveying device and document reading unit |
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KR20150047782A (en) * | 2013-10-25 | 2015-05-06 | 삼성전자주식회사 | Image forming apparatus |
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US10399805B2 (en) | 2015-01-09 | 2019-09-03 | Canon Kabushiki Kaisha | Sheet conveyance apparatus |
KR101955301B1 (en) * | 2015-01-22 | 2019-03-08 | 캐논 가부시끼가이샤 | Sheet conveyance apparatus and image forming apparatus |
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Also Published As
Publication number | Publication date |
---|---|
US8556259B2 (en) | 2013-10-15 |
JP5627384B2 (en) | 2014-11-19 |
US8387975B2 (en) | 2013-03-05 |
JP2012082057A (en) | 2012-04-26 |
CN102556703A (en) | 2012-07-11 |
US20130134654A1 (en) | 2013-05-30 |
CN102556703B (en) | 2015-05-13 |
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